mdbx: backport - Tweak MDB_PREV_MULTIPLE for uninit'd cursor.
mdbx: backport - Tweak MDB_PREV_MULTIPLE for uninit'd cursor.

Change-Id: I1f07e7c4d80631a1a0b2c70a936ef7b458baa11a

leo-yuriev/libfpta,leo-yuriev/libfpta