Disable systemd-run if the command is not found.

diff -Naur xpra-4.0.1/xpra/scripts/main.py xpra-4.0.1.patched/xpra/scripts/main.py
--- xpra-4.0.1/xpra/scripts/main.py	2020-05-17 18:12:15.000000000 +0200
+++ xpra-4.0.1.patched/xpra/scripts/main.py	2020-06-01 12:12:18.500257507 +0200
@@ -312,16 +312,18 @@
     if not is_systemd_pid1():
         return False
     #test it:
-    cmd = ["systemd-run", "--quiet", "--user", "--scope", "--", "true"]
-    proc = Popen(cmd, stdin=None, stdout=None, stderr=None, shell=False)
-    r = pollwait(proc, timeout=1)
-    if r is None:
-        try:
-            proc.terminate()
-        except Exception:
-            pass
-    return r==0
-
+    try:
+        cmd = ["systemd-run", "--quiet", "--user", "--scope", "--", "true"]
+        proc = Popen(cmd, stdin=None, stdout=None, stderr=None, shell=False)
+        r = pollwait(proc, timeout=1)
+        if r is None:
+            try:
+                proc.terminate()
+            except Exception:
+                pass
+        return r==0
+    except FileNotFoundError:
+        return False
 
 def run_mode(script_file, error_cb, options, args, mode, defaults):
     #configure default logging handler:
.scm?id=cba77ea9bd91707bfb00746876f36e5fb988b185'>tree</a><a href='/guix/commit/gnu.scm?id=cba77ea9bd91707bfb00746876f36e5fb988b185'>commit</a><a href='/guix/diff/gnu.scm?id=cba77ea9bd91707bfb00746876f36e5fb988b185'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu.scm'>
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<div class='path'>path: <a href='/guix/log/?id=cba77ea9bd91707bfb00746876f36e5fb988b185'>root</a>/<a href='/guix/log/gnu.scm?id=cba77ea9bd91707bfb00746876f36e5fb988b185'>gnu.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu.scm?id=cba77ea9bd91707bfb00746876f36e5fb988b185&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-07-25 19:11:37 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu.scm?id=d51bfe242fbe6f3f8f71d723e8fe0c7bbe711ba1'>Use 'formatted-message' instead of '&amp;message' where appropriate.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu.scm (%try-use-modules): Use 'formatted-message' instead of
'&amp;message'.
* gnu/machine/digital-ocean.scm (maybe-raise-unsupported-configuration-error):
Likewise.
* gnu/machine/ssh.scm (machine-check-file-system-availability): Likewise.
(machine-check-building-for-appropriate-system): Likewise.
(deploy-managed-host): Likewise.
(maybe-raise-unsupported-configuration-error): Likewise.
* gnu/packages.scm (search-patch): Likewise.
* gnu/services.scm (%service-with-default-value): Likewise.
(files-&gt;etc-directory): Likewise.
(fold-services): Likewise.
* gnu/system.scm (locale-name-&gt;definition*): Likewise.
* gnu/system/mapped-devices.scm (check-device-initrd-modules): Likewise.
(check-luks-device): Likewise.
* guix/channels.scm (latest-channel-instance): Likewise.
* guix/cve.scm (json-&gt;cve-items): Likewise.
* guix/git-authenticate.scm (commit-signing-key): Likewise.
(commit-authorized-keys): Likewise.
(authenticate-commit): Likewise.
(verify-introductory-commit): Likewise.
* guix/remote.scm (remote-pipe-for-gexp): Likewise.
* guix/scripts/graph.scm (assert-package): Likewise.
* guix/scripts/offload.scm (private-key-from-file*): Likewise.
* guix/ssh.scm (authenticate-server*): Likewise.
(open-ssh-session): Likewise.
(remote-inferior): Likewise.
* guix/ui.scm (matching-generations): Likewise.
* guix/upstream.scm (package-update): Likewise.
* tests/channels.scm ("latest-channel-instances, missing introduction for 'guix'"):
Catch 'formatted-message?'.
("authenticate-channel, wrong first commit signer"): Likewise.
* tests/lint.scm ("patches: not found"): Adjust message string.
* tests/packages.scm ("patch not found yields a run-time error"): Catch
'formatted-message?'.
* guix/lint.scm (check-patch-file-names): Handle 'formatted-message?'.
(check-derivation): Ditto.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-07-25 19:11:36 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu.scm?id=f9a8dd053c4e0fd1fc4b64291bb90de36520b3bc'>utils: Move '&amp;fix-hint' to (guix diagnostics).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/utils.scm (&amp;fix-hint): Move to...
* guix/diagnostics.scm (&amp;fix-hint): ... here.
* gnu.scm: Adjust imports accordingly.
* gnu/system/mapped-devices.scm: Likewise.
* guix/channels.scm: Likewise.
* guix/profiles.scm: Likewise.
* guix/scripts/system/reconfigure.scm: Likewise.
* guix/ssh.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-07-25 19:11:36 +0200'>2020-07-25</span></td><td><a href='/guix/commit/gnu.scm?id=a5e2fc73760a2ae023f2e56bdbf8025971f90e64'>utils: Move &lt;location&gt; and '&amp;error-location' to (guix diagnostics).</a><span class='msg-avail'>...<span class='msg-tooltip'>* guix/utils.scm (&lt;location&gt;, source-properties-&gt;location)
(location-&gt;source-properties, &amp;error-location): Move to...
* guix/diagnostics.scm: ... here.
* gnu.scm: Adjust imports accordingly.
* gnu/machine.scm: Likewise.
* gnu/system.scm: Likewise.
* gnu/tests.scm: Likewise.
* guix/inferior.scm: Likewise.
* tests/channels.scm: Likewise.
* tests/packages.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>