Fix possible buffer overflow

[kamahen]

This PR should be applied to branch develop.

These changes are because the compiler pointed out mis-use of strncmp() and memcpy(). I think that I've fixed the problems, but it's easy to make an off-by-one error in such code, so please review.

(A better way of fixing this would be to use std::string or std::basic_string<unsigned char>)

[kamahen]

The files to check are:

libhdt/src/libdcs/CSD_FMIndex.cpp
libhdt/src/libdcs/CSD_HTFC.cpp
libhdt/src/libdcs/CSD_PFC.cpp
libhdt/src/triples/TripleListDisk.cpp

The other files are straightforward responses to compiler warnings.

[kamahen]

The code now compiles cleanly using gcc-13.2 with -Wall -Wextra. There were some additional problems with the use of strncpy() that I fixed. (And, in an earlier commit, I hadn't correctly fixed a call to strncpy() -- I think it's correct now).
None of these compiler warnings resulted in any failures of the test cases, so I have no easy way of verifying that I've fixed anything, nor that I've fixed things correctly.

[kamahen]

This is ready to merge into branch develop. (using this? develop...JanWielemaker:hdt-cpp:develop-buffer)

Or I can do the merge on my local copy and push to branch develop ... it's up to you. (A 2nd pair of eyes, looking at my changes, is always appreciated)

Once that is done, I'll create a PR for the hdt pack that references this.