Fix #34256: join a mesh with non-uniform scale with another mesh showed wrong

normals, they need to be recalculated then.

source/blender/editors/mesh/meshtools.c

@@ -502,6 +502,9 @@ int join_mesh_exec(bContext *C, wmOperator *op)
 
 	/* tessface data removed above, no need to update */
 	mesh_update_customdata_pointers(me, FALSE);
+
+	/* update normals in case objects with non-uniform scale are joined */
+	ED_mesh_calc_normals(me);
 	
 	/* old material array */
 	for (a = 1; a <= ob->totcol; a++) {