MFC r298333:

MFC r298333:
r298333 (by cem):

Make Racct macro slightly more gracious given RACCT_UNDEFINED

rctl_string_to_rule could previously index below the zeroth element of
racct_types via the macro.  Maybe it shouldn't use the macro on
RACCT_UNDEFINED.  But given every other RACCT_ definition is non-negative, it
seems pretty easy to foot-shoot this one without the check.

CID:		1305574

git-svn-id: svn://svn.freebsd.org/base/stable/10@299616 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f