git-gui: avoid persisting modified author identity

Commit 7e71adc77f fixes a problem with git-gui failing to pick up the
original author identity during a commit --amend operation. However, the
new author details then become persistent for the remainder of the session.
This commit fixes this by ensuring the environment variables are reset
and the author information reset once the commit is completed.
The relevant changes were reworked to reduce global variables.

Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>
1 file changed