pg_dump: Have _EndLO report errno after CFH->write_func() failure

Other callers of that function do things this way, but this one didn't
get the memo.

src/bin/pg_dump/pg_backup_directory.c

@@ -697,7 +697,13 @@ _EndLO(ArchiveHandle *AH, TocEntry *te, Oid oid)
 	/* register the LO in blobs.toc */
 	len = snprintf(buf, sizeof(buf), "%u blob_%u.dat\n", oid, oid);
 	if (!CFH->write_func(buf, len, CFH))
-		pg_fatal("could not write to LOs TOC file");
+	{
+		/* if write didn't set errno, assume problem is no disk space */
+		if (errno == 0)
+			errno = ENOSPC;
+		pg_fatal("could not write to LOs TOC file: %s",
+				 CFH->get_error_func(CFH));
+	}
 }
 
 /*