git-issues show: Only print usage information if no ID or index is provided
git-issues show: Only print usage information if no ID or index is provided

Signed-off-by: Shawn Bohrer <af233bf5ee5ead96e21911c9207db6bbf8a7a886@gmail.com>

ktf/git-issues,mcepl/git-issues,duplys/git-issues