mmal/vout: Do not wait for picture in non-opaque mode

When not running in opaque mode the buffer headed over for rendering is only
returned when the following buffer isrendered or the component is disabled. So
in this case waiting for the buffer to be returned immediately deadlocks the
rendering. As all buffers get immediately flushed on stop it is safe to skip
this wait for non-opaque usecase.
Signed-off-by: Julian Scheel <julian@jusst.de>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/hw/mmal/vout.c

@@ -587,10 +587,12 @@ static void vd_display(vout_display_t *vd, picture_t *picture,
         maintain_phase_sync(vd);
     sys->next_phase_check = (sys->next_phase_check + 1) % PHASE_CHECK_INTERVAL;
 
-    vlc_mutex_lock(&sys->buffer_mutex);
-    while (atomic_load(&sys->buffers_in_transit) >= MAX_BUFFERS_IN_TRANSIT)
-        vlc_cond_wait(&sys->buffer_cond, &sys->buffer_mutex);
-    vlc_mutex_unlock(&sys->buffer_mutex);
+    if (sys->opaque) {
+        vlc_mutex_lock(&sys->buffer_mutex);
+        while (atomic_load(&sys->buffers_in_transit) >= MAX_BUFFERS_IN_TRANSIT)
+            vlc_cond_wait(&sys->buffer_cond, &sys->buffer_mutex);
+        vlc_mutex_unlock(&sys->buffer_mutex);
+    }
 }
 
 static int vd_control(vout_display_t *vd, int query, va_list args)