sql/catalog: avoid KV lookup for "" name

Sometimes the current DB is "". Normally we wouldn't try to resolve this
name, but if there's a mistake in name resolution logic, this check is a
simple way to avoid a KV lookup when we don't need it.

Release note: None

pkg/sql/catalog/catalogkv/namespace.go

@@ -168,6 +168,11 @@ func LookupObjectID(
 	parentSchemaID descpb.ID,
 	name string,
 ) (bool, descpb.ID, error) {
+	// Avoid a network round-trip if we accidentally ended up here without a
+	// name to look up.
+	if name == "" {
+		return false, descpb.InvalidID, nil
+	}
 	var key catalogkeys.DescriptorKey
 	if parentID == keys.RootNamespaceID {
 		key = catalogkeys.NewDatabaseKey(name)