Fix for bug #17457. This bug relates to files that have missing multires vertex data.

The fix is, if the file was saved on the highest multires level, then mesh contains a copy of the vertices anyway, and we can just copy it back into multires.

Otherwise, multires is removed from the mesh to avoid a crash.

source/blender/blenkernel/intern/multires.c

@@ -111,7 +111,8 @@ void multires_free(Multires *mr)
 			lvl= lvl->next;
 		}
 
-		MEM_freeN(mr->verts);
+		if(mr->verts)
+			MEM_freeN(mr->verts);
 
 		BLI_freelistN(&mr->levels);
 

source/blender/blenloader/intern/readfile.c

@@ -2876,6 +2876,18 @@ static void direct_link_mesh(FileData *fd, Mesh *mesh)
 			lvl->map_mem= NULL;
 		}
 	}
+
+	/* Gracefully handle corrupted mesh */
+	if(mesh->mr && !mesh->mr->verts) {
+		/* If totals match, simply load the current mesh verts into multires */
+		if(mesh->totvert == ((MultiresLevel*)mesh->mr->levels.last)->totvert)
+			mesh->mr->verts = MEM_dupallocN(mesh->mvert);
+		else {
+			/* Otherwise, we can't recover the data, silently remove multires */
+			multires_free(mesh->mr);
+			mesh->mr = NULL;
+		}
+	}
 	
 	if((fd->flags & FD_FLAGS_SWITCH_ENDIAN) && mesh->tface) {
 		TFace *tf= mesh->tface;