evr/sample: Avoid a race condition when releasing a tracked sample.

dlls/evr/sample.c

@@ -920,19 +920,21 @@ static ULONG WINAPI video_sample_AddRef(IMFSample *iface)
 static ULONG WINAPI video_sample_Release(IMFSample *iface)
 {
     struct video_sample *sample = impl_from_IMFSample(iface);
-    ULONG refcount;
+    ULONG refcount = InterlockedDecrement(&sample->refcount);
+    IMFAsyncResult *tracked_result = NULL;
 
     IMFSample_LockStore(sample->sample);
-    if (sample->tracked_result && sample->tracked_refcount == (sample->refcount - 1))
+    if (sample->tracked_result && sample->tracked_refcount == refcount)
     {
-        video_sample_tracking_thread_invoke(sample->tracked_result);
-        IMFAsyncResult_Release(sample->tracked_result);
+        tracked_result = sample->tracked_result;
+        video_sample_tracking_thread_invoke(tracked_result);
         sample->tracked_result = NULL;
         sample->tracked_refcount = 0;
     }
     IMFSample_UnlockStore(sample->sample);
 
-    refcount = InterlockedDecrement(&sample->refcount);
+    if (tracked_result)
+        IMFAsyncResult_Release(tracked_result);
 
     TRACE("%p, refcount %lu.\n", iface, refcount);