abbr doesn't kick in after tab

*I'm opening an issue rather than committing a fix directly because I'm not entirely certain what the default behavior should be in this scenario.*

If you have `abbr camcontrol "sudo camcontrol"` and then start a command with `camcontrol `, the prompt will update to `$ sudo camcontrol `, but if you instead type in part of the command name and let it autocomplete the rest,† e.g. `camcontrol` the prompt will change to `$ camcontrol ` with the abbreviation not kicking in.

I know there are basically two use cases for abbr, one for "shortcuts" and the other for typo corrections. I personally discourage the use of abbr for shortcuts and think that functions should be used, but I can see how completions wouldn't be taking abbr into account in that case. However for "typo" correction (`gti` -> `git`, `foo` -> `sudo foo`), I think we might want to check the abbr list post-completion for the sake of uniformity?

† here for the sake of reducing completion ambiguity the entirety of the command name will be typed in before completing