Fix for issue #2896

[its-mr-monday]

Credit to @Eponymous-One for finding the solution,

An issue was arising within the protocols.cc file where the following call within function nmap_getprotbynum:

//Line 194
assert(num >= 0 && num < UCHAR_MAX);

Was causing nmap to core dump
Resolving the issue by ensuring assert is checking it is actually hitting UCHAR_MAX and not 1 char short of UCHAR_MAX via:

assert(num >= 0 && num <= UCHAR_MAX);