don't crash http_access.log formatter on non-standard methods

Change-Id: I9b77a866f324eff78f733d97f3ac05212d40fd25
Reviewed-on: http://review.couchbase.org/44067
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>