The new rbt patch implementation did a pretty good job of applying commits from new-style review requests that have multi-commit history, but it broke with old review requests that just have single diffs. This change fixes up the issues I ran into: - The code was never populating the `commits` list, unless `--squashed` was given. It then would always use `commits[0]`, blowing up. I've changed it to fetch the full diff data when there are no commits. - When `--squashed` was specified, we'd end up passing `expand=None` to the API request, which would then blow up. - The code that determined whether to create the commit wasn't working properly with `--squashed`, because it was testing `patch_num` as if it was 0-indexed when in fact it's 1-indexed. Testing Done: - Was able to apply patches from review requests without commit history. - Was able to apply patches using `--squashed` - Ran unit tests (there are some problems with the test suite right now but those are unrelated to anything touched here).