fix: respect backslash-escaped quotes when splitting quoted parameters

[rajanpanth]

Summary

quoteCount() counts every literal DQUOTE to decide whether a comma/semicolon falls inside an open quoted-string, with no awareness of a preceding backslash. Per RFC 7230 §3.2.6, quoted-pair allows an escaped DQUOTE inside a quoted-string without closing it — so a parameter value containing \" throws off the parity count, and the parser thinks it's still inside a quoted string when the next media type begins.

var Negotiator = require('negotiator')
var n = new Negotiator({ headers: { accept: 'text/html;p="\\"", application/json' } })
n.mediaType(['application/json'])   // undefined -- should be 'application/json'

A perfectly valid Accept header that explicitly lists application/json gets it silently dropped, which could cause accepts/Express's res.format() to return a wrong-content-type response or a spurious 406.

Changes

• lib/mediaType.js: quoteCount() now walks the string char-by-char, skipping the character after any backslash instead of naively counting every DQUOTE.
• test/mediaType.js: two new cases alongside the existing unescaped-comma-in-quotes test (issue Fails to parse quoted parameters #36) — an escaped DQUOTE, and an escaped backslash immediately before a real closing DQUOTE (to confirm double-backslash doesn't false-positive).

Testing

• Full suite: 251/251 passing (3 pending, pre-existing/unrelated).
• eslint . clean.
• Manually verified before/after with the repro above.

[rajanpanth]

Friendly follow-up on this PR 👋

When you have a moment, could you please take a look? I’m happy to update anything if needed.

Thanks!