midx-write: put failing response value back

This instance of setting the result to 1 before going to cleanup was
accidentally removed in fcb2205 (midx: implement support for writing
incremental MIDX chains, 2024-08-06).

Signed-off-by: Derrick Stolee <stolee@gmail.com>

Author: derrickstolee

midx-write.c

@@ -1106,6 +1106,7 @@ static int write_midx_internal(struct repository *r, const char *object_dir,
 			m = m->base_midx;
 		}
 	} else if (ctx.m && fill_packs_from_midx(&ctx)) {
+		result = 1;
 		goto cleanup;
 	}