A bug in plyvel 0.2 -- reverse iterators with prefix are badly broken

gistfile1.py

#!/bin/env python3

import plyvel

db = plyvel.DB('/tmp/test-reverse-iterator.db', create_if_missing=True)

db.put(b'aaa', b'1')
db.put(b'bbb', b'2')

# these pass:
assert list(db.iterator(reverse=True))       == [(b'bbb', b'2'), (b'aaa', b'1')]
assert list(db.iterator(prefix=b'b'))        == [(b'bbb', b'2')]
assert list(db.iterator(prefix=b'c'))        == []
assert list(db.prefixed_db(b'c').iterator()) == []

# these fail:
assert list(db.iterator(prefix=b'c', reverse=True))      == []
assert list(db.prefixed_db(b'c').iterator(reverse=True)) == []

See wbolster/plyvel#9 for the accompanying bug report.