This allows proper clean-up after failing to apply a patch. Therefore,
if "git cl diff" ends up having conflict, it could be cleaned up.

BUG=438362

Review URL: https://codereview.chromium.org/896453002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@294679 0039d316-1c4b-4281-b951-d872f2087c98