when dereferencing a NULL pointer later on.
Choose to just check for the NULL pointer in the next for-loop for now to fix
the issue with a minimal amount of code churn
sys/queue.h use here would make more sense than using a static table
MFC after: 5 days
This avoids a segfault with malformed or unanticipated files,
like IPV6-TC.txt (a file containing just TEXTUAL-CONVENTIONS).
MFC after: 5 days
Found with: gensnmpdef /usr/local/share/snmp/mibs/IPV6-TC.txt