Fix no_git_dir UnboundLocalError in except block

In Python 3, exception blocks clean their variables up, and we get
a UnbloundLocalError when we try to reference the target outside
of the except block.

To pass the exception out we set a variable from the target.

Also pull --license above raising the error, as it should work
outside a git repo too.

https://www.python.org/dev/peps/pep-3110/#semantic-changes

Change-Id: I298ac3648068cd07c4cf232e32ab3daaaf8e549d

git_review/cmd.py

@@ -1418,8 +1418,8 @@ def _main():
                         yes=False)
     try:
         (top_dir, git_dir) = git_directories()
-    except GitDirectoriesException as no_git_dir:
-        pass
+    except GitDirectoriesException as _no_git_dir:
+        no_git_dir = _no_git_dir
     else:
         no_git_dir = False
         config = Config(os.path.join(top_dir, ".gitreview"))
@@ -1428,13 +1428,14 @@ def _main():
                             remote=None,
                             usepushurl=convert_bool(config['usepushurl']))
     options = parser.parse_args()
-    if no_git_dir:
-        raise no_git_dir
 
     if options.license:
         print(COPYRIGHT)
         sys.exit(0)
 
+    if no_git_dir:
+        raise no_git_dir
+
     if options.branch is None:
         branch = config['branch']
     else: