fix(MediaCap): Default video width and height to 1
fix(MediaCap): Default video width and height to 1

When querying MediaCapabilities.decodingInfo(), if the video width
or height is not present, set 1 as default. Linux Firefox would
claim the variant is unsupported via decodingInfo() if the values
are falsy.

Issue #1391

Change-Id: Idc27e6869a1276585a0ca35bd380e1b7ad1db242

tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player