Fixes

1. `Fix highlighting of non-empty second line` and `Fix highlighting of summary lines without trailing newlines` fix bugs that were just introduced in https://github.com/magit/git-modes/commit/f230bb7ea85dd642c55d7fd6101428abb9eaac53

2. To test commit `Fix matching of empty lines before summary`:
Enter a few newlines before the commit summary and notice the broken highlighting.