Fix kstring_t-related memory leaks
Fix kstring_t-related memory leaks

Each function uses just one _line_ variable, so no need to allocate it.
It's the kstring_t user's responsibility to call free(line.s) afterwards.

Also remember to close bgzf_fp in grab().

arq5x/grabix,arq5x/grabix,arq5x/grabix,arq5x/grabix