git-gui: Reorganized startup procedure to ensure gitdir is right.
git-gui: Reorganized startup procedure to ensure gitdir is right.

Because we cd after getting the cdup value from Git we can't try
to get the gitdir until after we perform the cd, as usually the
gitdir is relative to the current working directory.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>

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