Fix for crash when sculpting on multires object during playback

- Restored BLI_pbvh_grids_update stuff;
- Marc all nodes as changes in ED_sculpt_modifiers_changed, so
  draw_buffers would be keept correct.

source/blender/blenkernel/intern/subsurf_ccg.c

@@ -2251,8 +2251,16 @@ static struct PBVH *ccgDM_getPBVH(Object *ob, DerivedMesh *dm)
 	if(!ob->sculpt)
 		return NULL;
 
-	if(ob->sculpt->pbvh)
+	if(ob->sculpt->pbvh) {
+	   /* pbvh's grids, gridadj and gridfaces points to data inside ccgdm
+		  but this can be freed on ccgdm release, this updates the pointers
+		  when the ccgdm gets remade, the assumption is that the topology
+		  does not change. */
+		ccgdm_create_grids(dm);
+		BLI_pbvh_grids_update(ob->sculpt->pbvh, ccgdm->gridData, ccgdm->gridAdjacency, (void**)ccgdm->gridFaces);
+
 		ccgdm->pbvh = ob->sculpt->pbvh;
+	}
 
 	if(ccgdm->pbvh)
 		return ccgdm->pbvh;

source/blender/blenlib/BLI_pbvh.h

@@ -121,6 +121,8 @@ float BLI_pbvh_node_get_tmin(PBVHNode* node);
 void BLI_pbvh_update(PBVH *bvh, int flags, float (*face_nors)[3]);
 void BLI_pbvh_redraw_BB(PBVH *bvh, float bb_min[3], float bb_max[3]);
 void BLI_pbvh_get_grid_updates(PBVH *bvh, int clear, void ***gridfaces, int *totface);
+void BLI_pbvh_grids_update(PBVH *bvh, struct DMGridData **grids,
+	struct DMGridAdjacency *gridadj, void **gridfaces);;
 
 /* vertex deformer */
 float (*BLI_pbvh_get_vertCos(struct PBVH *pbvh))[3];

source/blender/blenlib/intern/pbvh.c

@@ -1475,6 +1475,13 @@ void BLI_pbvh_draw(PBVH *bvh, float (*planes)[4], float (*face_nors)[3], int smo
 	}
 }
 
+void BLI_pbvh_grids_update(PBVH *bvh, DMGridData **grids, DMGridAdjacency *gridadj, void **gridfaces)
+{
+	bvh->grids= grids;
+	bvh->gridadj= gridadj;
+	bvh->gridfaces= gridfaces;
+}
+
 float (*BLI_pbvh_get_vertCos(PBVH *pbvh))[3]
 {
 	int a;

source/blender/editors/sculpt_paint/sculpt.c

@@ -109,6 +109,16 @@ void ED_sculpt_modifiers_changed(Object *ob)
 		}
 
 		sculpt_free_deformMats(ob->sculpt);
+	} else {
+		PBVHNode **nodes;
+		int n, totnode;
+
+		BLI_pbvh_search_gather(ss->pbvh, NULL, NULL, &nodes, &totnode);
+
+		for(n = 0; n < totnode; n++)
+			BLI_pbvh_node_mark_update(nodes[n]);
+
+		MEM_freeN(nodes);
 	}
 }