When creating a new commit, there is no title, so the title checker
complains that the title isn't compliant and the commit cannot be
created if checkstyle is run as a pre-commit hook. Fix this by skipping
the title checker when run on staged changes.
Signed-off-by: Paul Elder <paul.elder@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>