WMF: don't return undefined value in Release() function.

The function was returning a member variable after the object was
deleted. Return a local copy instead.

Change-Id: I077e7e1c184ed0cfd4899a80c9147a2939c93cd7
Reviewed-by: Christian Stromme <christian.stromme@digia.com>

src/plugins/wmf/mfactivate.cpp

@@ -85,5 +85,5 @@ ULONG MFAbstractActivate::Release(void)
     ULONG cRef = InterlockedDecrement(&m_cRef);
     if (cRef == 0)
         delete this;
-    return m_cRef;
+    return cRef;
 }