@param b Pointer to the bam record
@param tag Desired aux tag
@return Pointer to the tag data, or NULL if tag is not present or on error
If the tag is not present, this function returns NULL and sets errno to
ENOENT. If the bam record's aux data is corrupt (either a tag has an
invalid type, or the last record is incomplete) then errno is set to
EINVAL and NULL is returned.
@param b Pointer to the bam record @param tag Desired aux tag @return Pointer to the tag data, or NULL if tag is not present or on error If the tag is not present, this function returns NULL and sets errno to ENOENT. If the bam record's aux data is corrupt (either a tag has an invalid type, or the last record is incomplete) then errno is set to EINVAL and NULL is returned.