Handling exception to call mppExecutorCleanup in standard_ExecutorStart (#12694)
Handling exception to call mppExecutorCleanup in standard_ExecutorStart (#12694)

According to a reported error in PolicyEagerFreeAssignOperatorMemoryKB makes                                                                                                                                                           query end without calling mppExecutorCleanup #12690, the code path in                                                                                                                                                                  `standard_ExecutorStart` didn't handle exception in
`PolicyAutoAssignOperatorMemoryKB` and `PolicyEagerFreeAssignOperatorMemoryKB`
calling, which may cause the OOM exception not to be handled in
`standard_ExecutorStart` but throw to upper `PortalStart` methods, while there
is also an exception handling mechanism in `PortalStart` but `mppExecutorCleanup`
will not call because `portal->queryDesc` will be `NULL` in certain transaction states.

This commit fixes it.
xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,lisakowen/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,greenplum-db/gpdb,50wu/gpdb,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb