git-gui: Fix removing non-pushable remotes

Git-gui does not add most of the remotes to the 'push' menu
since they are missing the "Push" line in their remotespec.
In that case, removing the remote would end up with an error.

Signed-off-by: Petr Baudis <pasky@suse.cz>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/remote.tcl

@@ -271,5 +271,6 @@ proc remove_remote {name} {
 	delete_from_menu $remote_m.fetch $name
 	delete_from_menu $remote_m.prune $name
 	delete_from_menu $remote_m.remove $name
-	delete_from_menu $remote_m.push $name
+	# Not all remotes are in the push menu
+	catch { delete_from_menu $remote_m.push $name }
 }