Fix GenomeCopySegmentsWhenSequencesOutOfOrderTest
Fix GenomeCopySegmentsWhenSequencesOutOfOrderTest

It was leaving the DNA string uninitialized, which is fine in HDF5 (it
just evaluates to whatever 0 is), but not fine in our current mmap code.

glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal,glennhickey/hal