virLogCleanerShutdown: Don't call g_regex_unref on NULL regex

Shutdown of virtlogd prints:

  (process:54742): GLib-CRITICAL **: 11:00:40.873: g_regex_unref: assertion 'regex != NULL' failed

Use g_clear_pointer instead which prevents it in the NULL case.

Fixes: 69eeef5dfbf
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

src/logging/log_cleaner.c

@@ -264,6 +264,5 @@ virLogCleanerShutdown(virLogHandler *handler)
         handler->cleanup_log_timer = -1;
     }
 
-    g_regex_unref(log_regex);
-    log_regex = NULL;
+    g_clear_pointer(&log_regex, g_regex_unref);
 }