[llvm-readelf] - Do not try to read past the end of the file when dumping the the SHT_GNU_HASH.

We have unobvious issue in the condition that is used to check
that we do not read past the EOF.

The problem is that the result of "GnuHashTable->nbuckets * 4" expression is uint32.
Because of that it was still possible to overflow it and pass the check.

There was no such problem with the "GnuHashTable->maskwords * sizeof(typename ELFT::Off)"
condition, because of `sizeof` on the right (which gives 64-bits value on x64),
but I've added an explicit conversion to 64-bit value for `GnuHashTable->maskwords` too.

Differential revision: https://reviews.llvm.org/D81103