git-am: do not allow empty commits by mistake.
git-am: do not allow empty commits by mistake.

Running "git-am --resolved" without doing anything can create an empty
commit. Prevent it.

Thanks for Eric W. Biederman for spotting this.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git