Toolchain-Utils: Fix bug when no files to lint/check

This CL fixes a bug in the previous one editing pre-submit which caused
presubmit to fail when no new files have been added.

BUG=None
TEST=created new branches, confirmed presubmit is run correctly

Change-Id: I1a1b968220e60db12d05bbdab25646bfe2eb42e0
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/1710022
Reviewed-by: George Burgess <gbiv@chromium.org>
Reviewed-by: Caroline Tice <cmtice@chromium.org>
Tested-by: Emma Vukelj <emmavukelj@google.com>
1 file changed