Fix style violations in syscache lookups.

Project style is to check the success of SearchSysCacheN and friends
by applying HeapTupleIsValid to the result.  A tiny minority of calls
creatively did it differently.  Bring them into line with the rest.

This is just cosmetic, since HeapTupleIsValid is indeed just a null
check at the moment ... but that may not be true forever, and in any
case it puts a mental burden on readers who may wonder why these
call sites are not like the rest.

Back-patch to v11 just to keep the branches in sync.  (The bulk of these
errors seem to have originated in v11 or v12, though a few are old.)

Per searching to see if anyplace else had made the same error
repaired in 62148c352.

src/backend/catalog/pg_publication.c

@@ -130,7 +130,7 @@ pg_relation_is_publishable(PG_FUNCTION_ARGS)
 	bool		result;
 
 	tuple = SearchSysCache1(RELOID, ObjectIdGetDatum(relid));
-	if (!tuple)
+	if (!HeapTupleIsValid(tuple))
 		PG_RETURN_NULL();
 	result = is_publishable_class(relid, (Form_pg_class) GETSTRUCT(tuple));
 	ReleaseSysCache(tuple);

src/backend/commands/indexcmds.c

@@ -1069,7 +1069,7 @@ DefineIndex(Oid relationId,
 
 				tup = SearchSysCache1(INDEXRELID,
 									  ObjectIdGetDatum(indexRelationId));
-				if (!tup)
+				if (!HeapTupleIsValid(tup))
 					elog(ERROR, "cache lookup failed for index %u",
 						 indexRelationId);
 				newtup = heap_copytuple(tup);

src/backend/commands/opclasscmds.c

@@ -1057,7 +1057,7 @@ assignOperTypes(OpFamilyMember *member, Oid amoid, Oid typeoid)
 
 	/* Fetch the operator definition */
 	optup = SearchSysCache1(OPEROID, ObjectIdGetDatum(member->object));
-	if (optup == NULL)
+	if (!HeapTupleIsValid(optup))
 		elog(ERROR, "cache lookup failed for operator %u", member->object);
 	opform = (Form_pg_operator) GETSTRUCT(optup);
 
@@ -1123,7 +1123,7 @@ assignProcTypes(OpFamilyMember *member, Oid amoid, Oid typeoid)
 
 	/* Fetch the procedure definition */
 	proctup = SearchSysCache1(PROCOID, ObjectIdGetDatum(member->object));
-	if (proctup == NULL)
+	if (!HeapTupleIsValid(proctup))
 		elog(ERROR, "cache lookup failed for function %u", member->object);
 	procform = (Form_pg_proc) GETSTRUCT(proctup);
 

src/backend/commands/operatorcmds.c

@@ -407,7 +407,7 @@ AlterOperator(AlterOperatorStmt *stmt)
 	oprId = LookupOperWithArgs(stmt->opername, false);
 	catalog = heap_open(OperatorRelationId, RowExclusiveLock);
 	tup = SearchSysCacheCopy1(OPEROID, ObjectIdGetDatum(oprId));
-	if (tup == NULL)
+	if (!HeapTupleIsValid(tup))
 		elog(ERROR, "cache lookup failed for operator %u", oprId);
 	oprForm = (Form_pg_operator) GETSTRUCT(tup);
 

src/backend/commands/tablecmds.c

@@ -7926,7 +7926,7 @@ CloneFkReferencing(Relation pg_constraint, Relation parentRel,
 		int			i;
 
 		tuple = SearchSysCache1(CONSTROID, parentConstrOid);
-		if (!tuple)
+		if (!HeapTupleIsValid(tuple))
 			elog(ERROR, "cache lookup failed for constraint %u",
 				 parentConstrOid);
 		constrForm = (Form_pg_constraint) GETSTRUCT(tuple);
@@ -7995,7 +7995,7 @@ CloneFkReferencing(Relation pg_constraint, Relation parentRel,
 			 */
 			partcontup = SearchSysCache1(CONSTROID,
 										 ObjectIdGetDatum(fk->conoid));
-			if (!partcontup)
+			if (!HeapTupleIsValid(partcontup))
 				elog(ERROR, "cache lookup failed for constraint %u",
 					 fk->conoid);
 			partConstr = (Form_pg_constraint) GETSTRUCT(partcontup);
@@ -15310,7 +15310,7 @@ ATExecDetachPartition(Relation rel, RangeVar *name)
 		Constraint *fkconstraint;
 
 		contup = SearchSysCache1(CONSTROID, ObjectIdGetDatum(fk->conoid));
-		if (!contup)
+		if (!HeapTupleIsValid(contup))
 			elog(ERROR, "cache lookup failed for constraint %u", fk->conoid);
 		conform = (Form_pg_constraint) GETSTRUCT(contup);
 
@@ -15650,9 +15650,8 @@ validatePartitionedIndex(Relation partedIdx, Relation partedTbl)
 
 		indTup = SearchSysCache1(INDEXRELID,
 								 ObjectIdGetDatum(inhForm->inhrelid));
-		if (!indTup)
-			elog(ERROR, "cache lookup failed for index %u",
-				 inhForm->inhrelid);
+		if (!HeapTupleIsValid(indTup))
+			elog(ERROR, "cache lookup failed for index %u", inhForm->inhrelid);
 		indexForm = (Form_pg_index) GETSTRUCT(indTup);
 		if (IndexIsValid(indexForm))
 			tuples += 1;

src/backend/optimizer/util/plancat.c

@@ -1335,7 +1335,7 @@ get_relation_statistics(RelOptInfo *rel, Relation relation)
 		int			i;
 
 		htup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(statOid));
-		if (!htup)
+		if (!HeapTupleIsValid(htup))
 			elog(ERROR, "cache lookup failed for statistics object %u", statOid);
 		staForm = (Form_pg_statistic_ext) GETSTRUCT(htup);