Incorrect reporting of error: This label's "for" attribute contains an ID that does not exist in the document. #187

Hi,

First of all many thanks for this tool, it's very useful indeed and the work put into it is greatly appreciated.

I came across bug #22 but I'm finding the same thing happening again on the live site (v2.0.7) when I paste a code snippet for evaluation. The snippet in question only has a label but actually has no for attribute (Google Maps code...). The bookmarked version of the CodeSniffer doesn't report this issue at all.