mdbxt: backport - fix 'db_dummy' inside mdbx_dbi_open_ex().
mdbxt: backport - fix 'db_dummy' inside mdbx_dbi_open_ex().

Change-Id: I70a21c9b77a43c5af749da5723fa965487a056b0

leo-yuriev/libfpta,leo-yuriev/libfpta