player: Avoid trying to join the player thread from itself

https://bugzilla.gnome.org/show_bug.cgi?id=796731
diff --git a/gst-libs/gst/player/gstplayer.c b/gst-libs/gst/player/gstplayer.c
index 5dd340a..5ab9e03 100644
--- a/gst-libs/gst/player/gstplayer.c
+++ b/gst-libs/gst/player/gstplayer.c
@@ -492,7 +492,10 @@
   if (self->loop) {
     g_main_loop_quit (self->loop);
 
-    g_thread_join (self->thread);
+    if (self->thread != g_thread_self ())
+      g_thread_join (self->thread);
+    else
+      g_thread_unref (self->thread);
     self->thread = NULL;
 
     g_main_loop_unref (self->loop);