source: mtbl_source_write(): don't ignore return value of mtbl_writer_add()
source: mtbl_source_write(): don't ignore return value of mtbl_writer_add()

snarkmaster/mtbl,rep/mtbl,farsightsec/mtbl,snarkmaster/mtbl,snarkmaster/mtbl,rep/mtbl,farsightsec/mtbl,rep/mtbl