Fix type comparison issue that is a hard error in GCC 10.

Taken from upstream:

  https://github.com/OpenTTD/grfcodec/commit/bb692b2c723c5e87cc8f89f445928e97594d5b8f

diff --git a/src/command.cpp b/src/command.cpp
index 9aa0e14..1f32cf1 100644
--- a/src/command.cpp
+++ b/src/command.cpp
@@ -300,8 +300,9 @@ bool parse_comment(const string&line){
 		break;
 	case BEAUTIFY:{
 		commandstream>>command_part;
-		uint val=find_command(command_part,beaut),togglebit;
-		if(val!=(uint)-1&&val!=OFF)_commandState.beautifier=true;
+		int val=find_command(command_part,beaut);
+		uint togglebit;
+		if(val!=-1&&val!=OFF)_commandState.beautifier=true;
 		switch(val){
 		case -1:
 			IssueMessage(0,COMMAND_INVALID_ARG,gen[BEAUTIFY].name);
@@ -372,7 +373,7 @@ bool parse_comment(const string&line){
 dotoggle:
 			commandstream>>command_part;
 			val=find_command(command_part,beaut);
-			if(!commandstream||val==(uint)-1){
+			if(!commandstream||val==-1){
 				IssueMessage(0,COMMAND_INVALID_ARG,gen[BEAUTIFY].name);
 				return true;
 			}

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<div class='path'>path: <a href='/guix/log/?id=1230a07fea29914a41067ca5b570a698b3efd684'>root</a>/<a href='/guix/log/gnu?id=1230a07fea29914a41067ca5b570a698b3efd684'>gnu</a>/<a href='/guix/log/gnu/services?id=1230a07fea29914a41067ca5b570a698b3efd684'>services</a>/<a href='/guix/log/gnu/services/cuirass.scm?id=1230a07fea29914a41067ca5b570a698b3efd684'>cuirass.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/services/cuirass.scm?id=1230a07fea29914a41067ca5b570a698b3efd684&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-10-23 21:48:51 +0200'>2019-10-23</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=b40f4a5995cff00077aa60881737d0d0f6871982'>services: cuirass: Create /var/log/cuirass during activation.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (cuirass-activation): Create "/var/log/cuirass".
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-09-23 23:41:19 +0200'>2019-09-23</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=46e552cb0f6b7b11600b7c41146f94dce70eee99'>services: cuirass: Remove unneeded conditional.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (cuirass-shepherd-service): Remove unneeded 'and'.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-08-29 08:06:54 +0200'>2019-08-29</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=3e7a62e2e40fc575d161e4c06ea2e333ab7df3b3'>services: cuirass: Log web interface to separate file.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (&lt;cuirass-configuration&gt;): Add web-log-file field.
(cuirass-shepherd-service): Read it and use it.
* doc/guix.texi (Continuous Integration): Document it.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-08-26 22:21:10 +0200'>2019-08-26</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=159b5e1f8a758e5754ea36929990f09436f4de47'>services: cuirass: Split into two separate services.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (cuirass-shepherd-service): Return two shepherd
services, one for the web interface, another for building packages.
</span></span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-03-04 15:22:58 +0100'>2019-03-04</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=56a93cb975ddc33d50183fb122e2aafda026f18e'>services: Use 'file-append' for user account shells.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (cuirass-account): Use 'file-append' instead
of #~(string-append #$shadow "/sbin/nologin").
* gnu/services/monitoring.scm (zabbix-server-account): Likewise.
(zabbix-agent-account): Likewise.
* gnu/services/rsync.scm (rsync-account): Likewise.
* gnu/services/ssh.scm (%openssh-accounts): Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-11-07 16:06:42 +0100'>2018-11-07</span></td><td><a href='/guix/commit/gnu/services/cuirass.scm?id=dcb45127e01ce2eeabc9270b64e817aa1d644672'>services: cuirass: Add 'ttl' configuration field.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/cuirass.scm (&lt;cuirass-configuration&gt;)[ttl]: New field.
(cuirass-shepherd-service): Honor it.
</span></span></td><td>Ludovic Courtès</td></tr>