Fix pg_dump to work against pre-9.0 servers again.

getBlobs' queries for pre-9.0 servers were broken in two ways:
the 7.x/8.x query uses DISTINCT so it can't have unspecified-type
NULLs in the target list, and both that query and the 7.0 one
failed to provide the correct output column labels, so that the
subsequent code to extract data from the PGresult would fail.

Back-patch to 9.6 where the breakage was introduced (by commit 23f34fa4).

Amit Langote and Tom Lane

Discussion: <0a3e7a0e-37bd-8427-29bd-958135862f0a@lab.ntt.co.jp>

src/bin/pg_dump/pg_dump.c

@@ -2875,19 +2875,20 @@ getBlobs(Archive *fout)
 	else if (fout->remoteVersion >= 90000)
 		appendPQExpBuffer(blobQry,
 						  "SELECT oid, (%s lomowner) AS rolname, lomacl, "
-						  "NULL AS rlomacl, NULL as initlomacl, "
-						  "NULL as initrlomacl "
+						  "NULL AS rlomacl, NULL AS initlomacl, "
+						  "NULL AS initrlomacl "
 						  " FROM pg_largeobject_metadata",
 						  username_subquery);
 	else if (fout->remoteVersion >= 70100)
 		appendPQExpBufferStr(blobQry,
-							 "SELECT DISTINCT loid, NULL::oid, NULL, "
-							 "NULL AS rlomacl, NULL AS initlomacl, "
-							 "NULL AS initrlomacl "
+							 "SELECT DISTINCT loid AS oid, "
+							 "NULL::name AS rolname, NULL::oid AS lomacl, "
+							 "NULL::oid AS rlomacl, NULL::oid AS initlomacl, "
+							 "NULL::oid AS initrlomacl "
 							 " FROM pg_largeobject");
 	else
 		appendPQExpBufferStr(blobQry,
-							 "SELECT oid, NULL::oid, NULL, "
+							 "SELECT oid, NULL AS rolname, NULL AS lomacl, "
 							 "NULL AS rlomacl, NULL AS initlomacl, "
 							 "NULL AS initrlomacl "
 							 " FROM pg_class WHERE relkind = 'l'");
@@ -2922,11 +2923,11 @@ getBlobs(Archive *fout)
 		binfo[i].initblobacl = pg_strdup(PQgetvalue(res, i, i_initlomacl));
 		binfo[i].initrblobacl = pg_strdup(PQgetvalue(res, i, i_initrlomacl));
 
-		if (PQgetisnull(res, i, i_lomacl) && PQgetisnull(res, i, i_rlomacl) &&
+		if (PQgetisnull(res, i, i_lomacl) &&
+			PQgetisnull(res, i, i_rlomacl) &&
 			PQgetisnull(res, i, i_initlomacl) &&
 			PQgetisnull(res, i, i_initrlomacl))
 			binfo[i].dobj.dump &= ~DUMP_COMPONENT_ACL;
-
 	}
 
 	/*