Escaped closing quote at end-of-input accepted as title close

My fuzzer found an interesting behaviour. The input: ``` markdown [f]: z "\" [f] ``` …is interpreted by cmark 0.31.2 as a valid link definition + reference: ``` html <p><a href="z" title="\">f</a></p> ``` This is valid HTML, but the CommonMark spec explicitly lists backslash escapes as working in link titles: * §6.3 says: "a `"` character only if it is backslash-escaped" * §2.4 lists backslash escapes as inert only in "code blocks, code spans, autolinks, or raw HTML." So strictly speaking, this input should probably fail to parse? Expected output: ``` html <p>[f]: z &quot;&quot;</p> <p>[f]</p> ``` Yes, this is ridiculous, but that's fuzzing for you.