Catch null pointer returns from PyCObject_AsVoidPtr and PyCObject_FromVoidPtr

This is reproducibly possible in Python 2.7 if the user turned
PendingDeprecationWarning into an error, but it's theoretically also possible
in earlier versions in case of exceptional conditions.

backpatched to 8.0

src/pl/plpython/plpython.c

 /**********************************************************************
  * plpython.c - python as a procedural language for PostgreSQL
  *
- *	$PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.148 2010/07/08 19:00:11 tgl Exp $
+ *	$PostgreSQL: pgsql/src/pl/plpython/plpython.c,v 1.149 2010/08/25 19:37:56 petere Exp $
  *
  *********************************************************************
  */
@@ -1315,6 +1315,8 @@ PLy_procedure_get(FunctionCallInfo fcinfo, Oid tgreloid)
 			elog(FATAL, "expected a PyCObject, didn't get one");
 
 		proc = PyCObject_AsVoidPtr(plproc);
+		if (!proc)
+			PLy_elog(ERROR, "PyCObject_AsVoidPtr() failed");
 		if (proc->me != plproc)
 			elog(FATAL, "proc->me != plproc");
 		/* did we find an up-to-date cache entry? */
@@ -1539,8 +1541,11 @@ PLy_procedure_create(HeapTuple procTup, Oid tgreloid, char *key)
 		PLy_procedure_compile(proc, procSource);
 
 		pfree(procSource);
+		procSource = NULL;
 
 		proc->me = PyCObject_FromVoidPtr(proc, NULL);
+		if (!proc->me)
+			PLy_elog(ERROR, "PyCObject_FromVoidPtr() failed");
 		PyDict_SetItemString(PLy_procedure_cache, key, proc->me);
 	}
 	PG_CATCH();