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;
 			}
d>
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<div class='path'>path: <a href='/guix/log/?id=bc4b2bd4954bffec3870a3981becb8cd182bacb0'>root</a>/<a href='/guix/log/gnu?id=bc4b2bd4954bffec3870a3981becb8cd182bacb0'>gnu</a>/<a href='/guix/log/gnu/services?id=bc4b2bd4954bffec3870a3981becb8cd182bacb0'>services</a>/<a href='/guix/log/gnu/services/kerberos.scm?id=bc4b2bd4954bffec3870a3981becb8cd182bacb0'>kerberos.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/kerberos.scm?id=bc4b2bd4954bffec3870a3981becb8cd182bacb0&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2017-03-12 19:09:32 +0100'>2017-03-12</span></td><td><a href='/guix/commit/gnu/services/kerberos.scm?id=720cb10c15a4606fe0dc3511db4fef325f3d9dc6'>services: Move configuration functions that shouldn't be factorized.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/configuration.scm (serialize-field, serialize-string)
(serialize-space-separated-string-list, space-separated-string-list?)
(serialize-file-name, file-name?, serialize-boolean): Move these functions...
* gnu/services/cups.scm: ...to this file.
* gnu/services/kerberos.scm: ...to this file.

Configuration syntaxes are very specific to services.  Some services may have
the same configuration syntax, but none of them is common enough to be
abstracted in configuration.scm.

Signed-off-by: Clément Lassieur &lt;clement@lassieur.org&gt;
</span></span></td><td>Clément Lassieur</td></tr>
<tr><td><span title='2016-12-03 18:00:32 +0100'>2016-12-03</span></td><td><a href='/guix/commit/gnu/services/kerberos.scm?id=8e3f813f224f948d74122b18016c7eccad95cbe1'>gnu: Add Kerberos client service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Kerberos Services)[Krb5 Service]: New subsubheading.
* gnu/services/kerberos.scm (krb5-service-type): New variable.
* gnu/services/configuration.scm (configuration-field-serializer,
  configuration-field-getter): Export variables.
</span></span></td><td>John Darrington</td></tr>
<tr><td><span title='2016-11-26 07:37:33 +0100'>2016-11-26</span></td><td><a href='/guix/commit/gnu/services/kerberos.scm?id=fc5dc4e81cacc4e0dcd81863e505ce5b314264c6'>gnu: Whitespace changes</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/services/kerberos.scm: Fold lines to 80 character limit.
</span></span></td><td>John Darrington</td></tr>
<tr><td><span title='2016-11-08 21:35:26 +0100'>2016-11-08</span></td><td><a href='/guix/commit/gnu/services/kerberos.scm?id=859e367d0709aac3c9a63610d7bb1adaba13d27b'>gnu: Add pam-krb5 service.</a><span class='msg-avail'>...<span class='msg-tooltip'>* doc/guix.texi (Kerberos Services): New node.
* gnu/services/kerberos.scm: New file.
* gnu/local.mk: Add it.
</span></span></td><td>John Darrington</td></tr>