Address infinite loop when processing $GENERATE
In nibble mode if the value to be converted was negative the parser would loop forever. Process the value as an unsigned int instead of as an int to prevent sign extension when shifting.
This was found by Eric Sesterhenn from X41.
Replaces https://gitlab.isc.org/isc-private/bind9/-/merge_requests/640
Closes #4353 (closed)
Edited by Mark Andrews