WMF: fix crash on media player destruction.

A race condition could cause a frame to be presented even after the
QAbstractVideoSurface was deleted. We now check that the surface is
valid before presenting a frame.

Task-number: QTBUG-41158
Change-Id: If593469a8267583e499e781336af38d3fbf318fd
Reviewed-by: Christian Stromme <christian.stromme@digia.com>

src/plugins/wmf/evrd3dpresentengine.cpp

@@ -330,6 +330,7 @@ void D3DPresentEngine::presentSample(void *opaque, qint64)
     IMFMediaBuffer* buffer = NULL;
     IDirect3DSurface9* surface = NULL;
 
+    if (m_surface && m_surface->isActive()) {
         if (sample) {
             // Get the buffer from the sample.
             hr = sample->GetBufferByIndex(0, &buffer);
@@ -359,6 +360,7 @@ void D3DPresentEngine::presentSample(void *opaque, qint64)
 
             m_surface->present(frame);
         }
+    }
 
 done:
     qt_wmf_safeRelease(&surface);