Merge commit 'c31f6b1d'

* commit 'c31f6b1d':
  avprobe: Print a user-friendly version of the display matrix
  avprobe: Support printing strings with empty keys

This commit is a noop. ffprobe is considerably different than avprobe
and is already printing display matrix values in a user readable way.
Merged-by: James Almer <jamrial@gmail.com>