amend! mfmediaengine: Be a bit more conservative with locks in engine…

… Shutdown.

mfmediaengine: Be a bit more conservative with locks in engine Shutdown.

During engine shutdown we acquire engine lock first, then locks of its constituents (e.g. sample
grabbers); whereas normally the order is the other way around (e.g. timer callback -> acquire sample
grabber lock -> OnProcessSample callback -> engine lock). This is deadlock prone.

With this commit, engine lock is released before we shutdown the inner media session.

dlls/mfmediaengine/main.c

@@ -2201,7 +2201,7 @@ static HRESULT WINAPI media_engine_GetVideoAspectRatio(IMFMediaEngineEx *iface,
 static HRESULT WINAPI media_engine_Shutdown(IMFMediaEngineEx *iface)
 {
     struct media_engine *engine = impl_from_IMFMediaEngineEx(iface);
-    IMFMediaSession *session;
+    IMFMediaSession *session = NULL;
     HRESULT hr = S_OK;
 
     TRACE("%p.\n", iface);
@@ -2218,8 +2218,11 @@ static HRESULT WINAPI media_engine_Shutdown(IMFMediaEngineEx *iface)
     }
     LeaveCriticalSection(&engine->cs);
 
-    IMFMediaSession_Shutdown(session);
-    IMFMediaSession_Release(session);
+    if (SUCCEEDED(hr))
+    {
+        IMFMediaSession_Shutdown(session);
+        IMFMediaSession_Release(session);
+    }
     return hr;
 }