coverity#441827 Deference before null check

In OutputDevice::ImplGlyphFallbackLayout we should check to ensure that
mpFontEntry is valid, if not then return NULL early.

Change-Id: I946aa4d724a73a2ff85a4281c0df5f75e12104f7
Fix 6b431b1f0d397067504b5300d49e10e232936836

Pushed wrong branch. Oops, sorry.

Change-Id: I592cf16c7af3c5e37a03eee79e5822dcc0b39225