playbin3: fix leak of recursive mutex
diff --git a/gst/playback/gstplaybin3.c b/gst/playback/gstplaybin3.c
index d5cc5d1..edb77bd 100644
--- a/gst/playback/gstplaybin3.c
+++ b/gst/playback/gstplaybin3.c
@@ -1421,6 +1421,7 @@
   if (playbin->velements)
     g_sequence_free (playbin->velements);
 
+  g_rec_mutex_clear (&playbin->activation_lock);
   g_rec_mutex_clear (&playbin->lock);
   g_mutex_clear (&playbin->dyn_lock);
   g_mutex_clear (&playbin->elements_lock);