BUG/MINOR: http: abort request processing on filter failure

BUG/MINOR: http: abort request processing on filter failure

Commit c600204 ("BUG/MEDIUM: regex: fix risk of buffer overrun in
exp_replace()") added a control of failure on the response headers,
but forgot to check for the error during request processing. So if
the filters fail to apply, we could keep the request. It might
cause some headers to silently fail to be added for example. Note
that it's tagged MINOR because a standard configuration cannot make
this case happen.

The fix should be backported to 1.5 and 1.4 though.