lmdb: ITS#7377 Catch mdb_put() to blocked/read-only txns.
lmdb: ITS#7377 Catch mdb_put() to blocked/read-only txns.

...early enough that txn state is left unchanged.

Change-Id: Ia475660f339f7b741eaaa126978f8419a19b67a0

leo-yuriev/libfpta,leo-yuriev/libfpta