Fix ExecuteCallStmt to not scribble on the passed-in parse tree.
Fix ExecuteCallStmt to not scribble on the passed-in parse tree.

Modifying the parse tree at execution time is, or at least ought to be,
verboten.  It seems quite difficult to actually cause a crash this way
in v11 (although you can exhibit it pretty easily in HEAD by messing
with plan_cache_mode).  Nonetheless, it's risky, so fix and back-patch.

Discussion: f07ecd432272f9da03eb9078a5ac2b0a3ea39c7d@sss.pgh.pa.us

adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,xinzweb/gpdb,50wu/gpdb,50wu/gpdb,xinzweb/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,greenplum-db/gpdb,adam8157/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,50wu/gpdb