core: fix memory leak on /upgrade when file signature in upgrade file is invalid

ChangeLog.asciidoc

@@ -15,6 +15,8 @@ http://weechat.org/files/releasenotes/ReleaseNotes-devel.html[release notes]
 
 == Version 1.0 (under dev)
 
+* core: fix memory leak on /upgrade when file signature in upgrade file is
+  invalid
 * core: fix memory leak in completion of config options values
 * core: fix memory leak when removing script files
 * core: fix result of hash function (in hashtables) on 32-bit systems

src/core/wee-upgrade-file.c

@@ -759,6 +759,8 @@ upgrade_file_read (struct t_upgrade_file *upgrade_file,
     {
         UPGRADE_ERROR(_("read - bad signature (upgrade file format may have "
                         "changed since last version)"), "");
+        if (signature)
+            free (signature);
         return 0;
     }