Fix double mutex lock and double free

Index: plugins/vnc/vnc_plugin.c
--- plugins/vnc/vnc_plugin.c.orig
+++ plugins/vnc/vnc_plugin.c
@@ -114,8 +114,6 @@ static void onMainThread_schedule_callback_and_wait(st
 	pthread_mutex_lock(&d->mu);
 	gdk_threads_add_idle((GSourceFunc)onMainThread_cb, (gpointer)d);
 
-	pthread_mutex_lock(&d->mu);
-
 	pthread_cleanup_pop(0);
 	pthread_mutex_unlock(&d->mu);
 	pthread_mutex_destroy(&d->mu);
@@ -240,7 +238,6 @@ static void remmina_plugin_vnc_update_scale(RemminaPro
 		d->gp = gp;
 		d->scale = scale;
 		onMainThread_schedule_callback_and_wait(d);
-		g_free(d);
 		return;
 	}