Enabled workaround to solve threading issues in draw manager

This workaround addresses T79533 and T79038 for Blender 2.90. The
solution isn't clear and needs more research and work. In order to
continue with blender 2.90 release it was proposed to add this work
around.

It has been tested with the test files provided in the reports.

Reviewed By: Dalai Felinto, Clément Foucault

Differential Revision: https://developer.blender.org/D8695

source/blender/draw/intern/draw_cache_impl_mesh.c

@@ -1549,6 +1549,9 @@ void DRW_mesh_batch_cache_create_requested(struct TaskGraph *task_graph,
                                      scene,
                                      ts,
                                      use_hide);
+  /* TODO(jbakker): Work-around for threading issues in 2.90. See T79533, T79038. Needs to be
+   * solved or made permanent in 2.91. Underlying issue still needs to be researched. */
+  BLI_task_graph_work_and_wait(task_graph);
 #ifdef DEBUG
   drw_mesh_batch_cache_check_available(task_graph, me);
 #endif