[Feature] Add "reject no match" support

[MithicSpirit]

Would be nice if bemenu had a flag to prevent output that does not match any of the inputs. This should work similarly to these two dmenu patches together: reject no match and restrict return. Together, these two patches both prevent the user from inputting text that has no resulting matches and from using S-RET to print the current filter text (which often does not match exactly with any of the options).

These are primarily useful for using bemenu as a form of interface/selection screen, where invalid inputs are nonsensical.

[merrittlj]

By "reject no match", you mean not allowing the user to input filter text that would result in no matches? This seems pretty easy to implement, if this is what you mean exactly.

[MithicSpirit]

Yes, though I think that it would also be useful to be able to disable S-RET and selecting multiple options (as a separate flag like in dmenu, or combined into the same flag as reject no match). Those sound even easier to do.

[Co3co]

Are there plans to implement this? It's been a while since the issue was opened.