Fix add_version () core dump on acquiring delta (#788)
Fix add_version () core dump on acquiring delta (#788)

SchemaChange convert segment groups in reverse.
So SegmentGroup with segment_group_id = 1 may be handled
before SegmentGroup with segment_group_id = 0.
This will leads to acquiring delta not be allocated.
It will be core dump in SIGSEGV.
imay/palo,imay/palo,imay/palo,imay/palo,imay/palo,imay/palo