urisourcebin: Clear pad from pending list if it was linked

If not, the other slots might try to link the pad again.
This can happen when the demuxer has multiple src pads
and their caps are identical

https://bugzilla.gnome.org/show_bug.cgi?id=777121

gst/playback/gsturisourcebin.c

@@ -1049,6 +1049,8 @@ link_pending_pad_to_output (GstURISourceBin * urisrc, OutputSlotInfo * slot)
       out_info->output_slot = slot;
       slot->linked_info = out_info;
       res = TRUE;
+      urisrc->pending_pads =
+          g_list_remove (urisrc->pending_pads, out_info->demux_src_pad);
     } else {
       GST_ERROR_OBJECT (urisrc,
           "Failed to link new demuxer pad to the output slot we tried");