mf: Leave instead of enter a critical section.

dlls/mf/samplegrabber.c

@@ -1040,7 +1040,7 @@ static HRESULT WINAPI sample_grabber_sink_Shutdown(IMFMediaSink *iface)
         IMFStreamSink_Release(&grabber->stream->IMFStreamSink_iface);
         grabber->stream = NULL;
     }
-    EnterCriticalSection(&grabber->cs);
+    LeaveCriticalSection(&grabber->cs);
 
     return hr;
 }