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). Build upon a test that already deletes
a packfile to verify that this error propagates to full command failure.

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

Author: derrickstolee

midx-write.c

@@ -1104,6 +1104,7 @@ 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;
 	}
 

t/t5319-multi-pack-index.sh

@@ -1100,7 +1100,10 @@ test_expect_success 'load reverse index when missing .idx, .pack' '
 		mv $idx.bak $idx &&
 
 		mv $pack $pack.bak &&
-		git cat-file --batch-check="%(objectsize:disk)" <tip
+		git cat-file --batch-check="%(objectsize:disk)" <tip &&
+
+		test_must_fail git multi-pack-index write 2>err &&
+		grep "could not load pack" err
 	)
 '