tdb: Make robust against shrinking tdbs

tdb: Make robust against shrinking tdbs

When probing for a size change (eg. just before tdb_expand, tdb_check,
tdb_rescue) we call tdb_oob(tdb, tdb->map_size, 1, 1).  Unfortunately
this does nothing if the tdb has actually shrunk, which as Volker
demonstrated, can actually happen if a "longlived" parent crashes.

So move the map/update size/remap before the limit check.