Merge branch 'as/shallow-slab-use-fix'

Correct code that tried to reference all entries in a sparse array
of pointers by mistake.

* as/shallow-slab-use-fix:
  shallow.c: don't free unallocated slabs

shallow.c

@@ -156,6 +156,8 @@ struct commit_list *get_shallow_commits(struct object_array *heads, int depth,
 	for (i = 0; i < depths.slab_count; i++) {
 		int j;
 
+		if (!depths.slab[i])
+			continue;
 		for (j = 0; j < depths.slab_size; j++)
 			free(depths.slab[i][j]);
 	}