BZ#14498: fix infinite loop in nss_db_getservbyname

nss_db uses nss_files code for services, but a continue on protocol
mismatch that doesn't affect nss_files skipped the code that advanced
to the next db entry.  Any one of these changes would suffice to fix
it, but fixing both makes them both safer to reuse elsewhere.

for  ChangeLog

	[BZ #14498]
	* NEWS: Fixed.
	* nss/nss_db/db-XXX.c (_nss_db_get##name##_r): Update hidx
	after parsing line but before break_if_match.
	* nss/nss_files/files-service (DB_LOOKUP): Don't "continue;"
	if there is a protocol mismatch.