Fix a bug in LoadFlexiNexus picked up by MSVC in debug

vector::reserve only pre-allocates memory, it doesn't expand the size
of the vector meaning subscripting is technically not valid. Release builds
will allow it as the memory is there so the underlying array can still be
addressed.
Refs #7505
Cull more warnings from SINQ library.

Refs #7505
Merge branch 'feature/7505_sinq_code_check' into develop