Fix catastrophic backtracking issue in header parsing regular expression.
Fix catastrophic backtracking issue in header parsing regular expression.

The affected pattern is only used from a single non-public function,
which in turn is not actually used anywhere. It's in dead code. No
security issue.

fkazimierczak/bottle,defnull/bottle,oz123/bottle,fkazimierczak/bottle,defnull/bottle,bottlepy/bottle,bottlepy/bottle,oz123/bottle