Problem was that verify_constraints() didn't check if
there was an error as part of evaluating constraints
(can happen in strict mode).

In one-row-insert the error was ignored when using
binary logging as binary logging clear errors if insert
succeeded. In multi-row-insert the error was noticed
for the second row.

After this fix one will get an error for both one and
multi-row inserts if the constraints generates a warning
in strict mode.