android/avrcp: Fix warnings when freeing avrcp_device struct

If the device does not yet have queue due to not have a session it cause
the following warnings when avrcp_device_free is called:
(bluetoothd:1102): GLib-CRITICAL **: g_queue_foreach: assertion 'queue != NULL' failed
(bluetoothd:1102): GLib-CRITICAL **: g_queue_free: assertion 'queue != NULL' failed
diff --git a/android/avrcp.c b/android/avrcp.c
index 911b1df..1d211ad 100644
--- a/android/avrcp.c
+++ b/android/avrcp.c
@@ -442,8 +442,10 @@
 {
 	struct avrcp_device *dev = data;
 
-	g_queue_foreach(dev->queue, (GFunc) g_free, NULL);
-	g_queue_free(dev->queue);
+	if (dev->queue) {
+		g_queue_foreach(dev->queue, (GFunc) g_free, NULL);
+		g_queue_free(dev->queue);
+	}
 
 	if (dev->session)
 		avrcp_shutdown(dev->session);