Make `has_modifier()` return `true` for linear modifiers

[ids1024]

has_modifier() is used in two places. One has a special case for linear modifiers (which could handled specially regardless of what has_modifier() returns. The other use doesn't handle linear in any special way, and is probably incorrect, though drivers may tend to work with it anyway.

Implicit modifiers are not in general linear, so semantically this didn't make much sense.

Leaving as a draft, since I'm not actually sure what this breaks or fixes in practice. There may be a reason it was done this way.