Fix stateful NON_LATIN1_REGEXP in createparams

[deepview-autofix]

The module-level NON_LATIN1_REGEXP has the /g flag, so calling .test(fallback) leaves lastIndex at the match position. A subsequent create() call with a non-ISO-8859-1 fallback would resume matching from that stale index, could miss earlier non-latin1 characters, and silently bypass the "fallback must be ISO-8859-1 string" validation - producing a Content-Disposition with non-latin1 bytes in filename=.

Reset lastIndex to 0 before the .test call to keep the validation deterministic across invocations.

[ChALkeR]

This is mine

Prior to the fix:

> require('content-disposition')('1.pdf', { fallback: '😭' })
Uncaught TypeError: fallback must be ISO-8859-1 string
> require('content-disposition')('1.pdf', { fallback: '😭' })
Uncaught TypeError: fallback must be ISO-8859-1 string
> require('content-disposition')('1.pdf', { fallback: '😭' })
`attachment; filename="😭"; filename*=UTF-8''1.pdf`

[blakeembrey]

It looks like this is an issue in the current released code, want to make a PR against 1.x branch instead? In the current main, that code will be going out in 2.x and I think it should just remove the /g flag, but it depends on a bunch of other PRs being merged first (including the refactor to not use regexes).

[ChALkeR]

@blakeembrey will do