submodule: fix leaking submodule ODB paths

In `add_submodule_odb_by_path()` we add a path into a global string
list. The list is initialized with `NODUP`, which means that we do not
pass ownership of strings to the list. But we use `xstrdup()` when we
insert a path, with the consequence that the string will never get
free'd.

Plug the leak by marking the list as `DUP`. There is only a single
callsite where we insert paths anyway, and as explained above that
callsite was mishandling the allocation.

This leak is exposed by t7814, but plugging it does not make the whole
test suite pass.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

submodule.c

@@ -175,11 +175,11 @@ void stage_updated_gitmodules(struct index_state *istate)
 		die(_("staging updated .gitmodules failed"));
 }
 
-static struct string_list added_submodule_odb_paths = STRING_LIST_INIT_NODUP;
+static struct string_list added_submodule_odb_paths = STRING_LIST_INIT_DUP;
 
 void add_submodule_odb_by_path(const char *path)
 {
-	string_list_insert(&added_submodule_odb_paths, xstrdup(path));
+	string_list_insert(&added_submodule_odb_paths, path);
 }
 
 int register_all_submodule_odb_as_alternates(void)