Bug 1821803 - part3 : set size on the streamBlob. r=jolin

The ctor for the nsTArray only sets the capacity, not size, so we need
to set it explicitly.

Differential Revision: https://phabricator.services.mozilla.com/D172488

dom/media/platforms/wmf/MFPMPHostWrapper.cpp

@@ -38,7 +38,8 @@ STDMETHODIMP MFPMPHostWrapper::ActivateClassById(LPCWSTR aId, IStream* aStream,
     STATSTG statstg;
     RETURN_IF_FAILED(
         aStream->Stat(&statstg, STATFLAG_NOOPEN | STATFLAG_NONAME));
-    nsTArray<uint8_t> streamBlob(statstg.cbSize.LowPart);
+    nsTArray<uint8_t> streamBlob;
+    streamBlob.SetLength(statstg.cbSize.LowPart);
     unsigned long readSize = 0;
     RETURN_IF_FAILED(
         aStream->Read(&streamBlob[0], streamBlob.Length(), &readSize));