[OPENJPA-2986] Let setTimeout(null) clear a query timeout

[rzo1]

Query.setTimeout(null) passed the null straight to setHint(), which drove it through FetchConfigurationImpl.setHint() into a reflective call of setQueryTimeout(int) and failed with a bad-hint-value IllegalArgumentException. So a timeout set through this API could never be cleared — on queries it did not silently ignore the null, it threw — and getTimeout() kept reporting the stale value.

A null timeout now restores the timeout the query inherits from its entity manager, which is what the query would have used had setTimeout() never been called. Deliberately not FetchPlan.DEFAULT, which resolves to the OpenJPAConfiguration value and would discard an entity-manager-scoped timeout the caller never set here.

getTimeout() reports the effective fetch plan value rather than the recorded hint, so it cannot disagree with what the query will actually use, and StoredProcedureQueryImpl delegates both methods to its query so the two cannot drift apart.

EntityManagerImpl carries a setTimeout/getTimeout pair too, but those implement EntityTransaction — a transaction timeout in seconds — and are left alone here.