Fix pg_dump output to a named tar-file archive.

"pg_dump -Ft -f filename ..." got broken by my recent commit
4317e0246c, which I fear I only tested
in the output-to-stdout variant.

Report and fix by Muhammad Asif Naeem.

src/bin/pg_dump/pg_backup_tar.c

@@ -862,6 +862,7 @@ _CloseArchive(ArchiveHandle *AH)
 
 		ropt = NewRestoreOptions();
 		memcpy(ropt, AH->ropt, sizeof(RestoreOptions));
+		ropt->filename = NULL;
 		ropt->dropSchema = 1;
 		ropt->compression = 0;
 		ropt->superuser = NULL;