tools: ratbagctl.devel: fix exception if the given arguments are wrong

"sudo ./build/ratbagctl.devel profile 2 4" returns an exception with cmd
being unknown.

Signed-off-by: Benjamin Tissoires <benjamin.tissoires@gmail.com>

tools/ratbagctl.devel.in

@@ -45,6 +45,8 @@ def main(argv):
     parser.want_keepalive = True
     print('export RATBAGCTL_DEVEL="{}"\n'.format(os.environ['RATBAGCTL_DEVEL']))
 
+    cmd = None
+
     try:
         cmd = parser.parse(argv)
         cmd.func(ratbagd, cmd)
@@ -54,6 +56,8 @@ def main(argv):
                 signal.pause()
         except KeyboardInterrupt:
             pass
+        except AttributeError:  # in case the parsing failed and cmd is None
+            pass
         toolbox.terminate_ratbagd(ratbagd_process)