Fix T72175: DrawManager Crash Large Objects

Introduced by 9c337fcfe2 mistaken that `MeshExtract.use_threading` set
to false means that no threading is used at all. This is not the case it
will still perform threading for large objects, it will only run the
different subtasks in serial.

Fixed by scheduling the `lines_loose` in the task_pool after the rest
have been executed. This is cleaner than the previous implementation as
it sticks more to the actual design.

source/blender/draw/intern/draw_cache_extract_mesh.c

@@ -4483,20 +4483,22 @@ void mesh_buffer_cache_create_requested(MeshBatchCache *cache,
   EXTRACT(ibo, edituv_points);
   EXTRACT(ibo, edituv_fdots);
 
-#undef EXTRACT
-
   /* TODO(fclem) Ideally, we should have one global pool for all
    * objects and wait for finish only before drawing when buffers
    * need to be ready. */
   BLI_task_pool_work_and_wait(task_pool);
-  BLI_task_pool_free(task_pool);
+
+  /* The next task(s) rely on the result of the tasks above. */
 
   /* The `lines_loose` is a sub buffer from `ibo.lines`.
-   * We don't use the extract mechanism due to potential synchronization issues.*/
-  if (mbc.ibo.lines_loose) {
-    extract_task_create(NULL, mr, &extract_lines_loose, mbc.ibo.lines_loose, task_counters);
-  }
+   * We schedule it here due to potential synchronization issues.*/
+  EXTRACT(ibo, lines_loose);
 
+  BLI_task_pool_work_and_wait(task_pool);
+
+#undef EXTRACT
+
+  BLI_task_pool_free(task_pool);
   MEM_freeN(task_counters);
 
   mesh_render_data_free(mr);