🐛 blame parser fails with `-b` / `blankBoundary`

[adamchainz]

Similar to #1171. It seems the blame parser also isn’t ready for lines with no commit information at the start, from the -b option / blankBoundary configuration option.

Here’s an example from the Django repository, providing --since so that there’s a boundary. First, the following is correctly parsed with delta:

$ git --no-pager blame -L 1,1 --since yesterday django/utils/html.py
^facc153af7 (sarahboyce 2023-04-06 19:40:14 +0200 1) """HTML utilities suitable for global use."""

…which looks like:

$ git blame -L 1,1 --since yesterday django/utils/html.py
4 months ago    sarahboyce      ^facc153af7│  1 │ """HTML utilities suitable for global use."""

Second, adding -b changes Git to not output any commit information for those beyond the boundary (previously indicated by the ^):

$ git --no-pager blame -L 1,1 --since yesterday -b django/utils/html.py
            (sarahboyce 2023-04-06 19:40:14 +0200 1) """HTML utilities suitable for global use."""

…which delta fails to highlight:

$ git blame -L 1,1 --since yesterday -b django/utils/html.py
            (sarahboyce 2023-04-06 19:40:14 +0200 1) """HTML utilities suitable for global use."""

(This is a shame because the oh-my-zsh aliases set -b by default: https://github.com/ohmyzsh/ohmyzsh/blob/03a0d5bbaedc732436b5c67b166cde954817cc2f/plugins/git/git.plugin.zsh#L118 . Though I just made a PR to remove that: https://github.com/ohmyzsh/ohmyzsh/pull/11864 .)

• [x] Please include the raw text output from git, so that we can reproduce the problem. (You can use git --no-pager to produce the raw text output.)
• [-] A screenshot of Delta's output is often helpful also.

Thanks for filing a Delta bug report!