change size_t to uint32_t in bam_header_t
change size_t to uint32_t in bam_header_t

This may cause issues on 64-bit big-endian machines. Reported and fixed by Paolo Emilio Mazzon.

AngieHinrichs/samtabix,lh3/samtools,AngieHinrichs/samtabix,lh3/samtools,lh3/samtools,AngieHinrichs/samtabix,AngieHinrichs/samtabix,AngieHinrichs/samtabix