Fix platforms that don't support PVI_NumAdapters

Not all platforms currently support the PVI_NumAdapters query from
PlatformVideoInfo.  This fix puts in the assumption that there is always
1 adapter if the PVI_NumAdapaters query returns false.  This was the
behaviour prior to PVI_NumAdapters being put in place.
Merge pull request #320 from DavidWyand-GG/PlatformVideoInfoFix

Fix platforms that don't support PVI_NumAdapters