fix a crash and a leak.

fix a crash and a leak.
4.1.15 (client) -> 5.x (server) because of the incompatibility because of
decimal in the protocol binding may fail. Don't close the statement in
that case because subsequent ->execute() will crash or any other function
that will try to use already freed (and in debug mode thrashed) pointer.
#probably more problems exist because of the 4.1.x -> 5.x protocol
#incompatibility