Fix T75607: crash trying to sculpt while remesh is in progress

The interface is already locked, but the paint brush drawing could stll be
reading the mesh that was being edited in another thread.

source/blender/windowmanager/intern/wm_draw.c

@@ -84,6 +84,13 @@ static void wm_paintcursor_draw(bContext *C, ScrArea *area, ARegion *region)
   bScreen *screen = WM_window_get_active_screen(win);
   wmPaintCursor *pc;
 
+  /* Don't draw paint cursors with locked interface. Painting is not possible
+   * then, and cursor drawing can use scene data that another thread may be
+   * modifying. */
+  if (wm->is_interface_locked) {
+    return;
+  }
+
   if (region->visible && region == screen->active_region) {
     for (pc = wm->paintcursors.first; pc; pc = pc->next) {