d3d: d3d_wnd_proc (d3dhelper.c) raises an exception because sink is NULL at LOCK_SINK (sink);

Submitted by Marcos Kintschner

At the function d3d_wnd_proc in the d3dhelper.c file, GetProp returns NULL at this code:

GstD3DVideoSink *sink =
(GstD3DVideoSink *) GetProp (hWnd, TEXT ("GstD3DVideoSink"));

Then it calls LOCK_SINK(NULL) here:

LOCK_SINK (sink);
proc = sink->d3d.orig_wnd_proc;
UNLOCK_SINK (sink);

And the program crashes at function g_rec_mutex_get_impl in the gthread-win32.c file.

Version: 1.14.2