Fix an UnboundLocalError when using --diff-filename.

Review Request #7482 — Created July 3, 2015 and submitted — Latest diff uploaded

Information

RBTools
release-0.6.x
9d95189...

Reviewers

The calculation of the changenum/commit ID was trying to reference a variable
that wasn't set using --diff-filename. This change fixes it.

Posted this change using --diff-filename.