ui: Don't check for mode change after mouse_set error

hmp_mouse_set() doesn't bail out when it can't find a mouse.
Harmless, since qemu_input_check_mode_change() should be a no-op then.
Clean it up anyway.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230109190321.1056914-16-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

ui/input.c

@@ -616,6 +616,7 @@ void hmp_mouse_set(Monitor *mon, const QDict *qdict)
 
     if (!found) {
         error_report("Mouse at index '%d' not found", index);
+        return;
     }
 
     qemu_input_check_mode_change();