Fixed the "Enable modifier during editmode" button for the case when there are

only deform modifiers in the stack. The code that copied the cage mesh to the
final mesh didn't check for vertex coordinates; I have added this check.

source/blender/blenkernel/intern/DerivedMesh.c

@@ -2024,7 +2024,7 @@ static void editmesh_calc_modifiers(DerivedMesh **cage_r,
 		CDDM_calc_normals(*final_r);
 	} else if (dm) {
 		*final_r = dm;
-	} else if (cage_r && *cage_r) {
+	} else if (!deformedVerts && cage_r && *cage_r) {
 		*final_r = *cage_r;
 	} else {
 		*final_r = getEditMeshDerivedMesh(em, ob, deformedVerts);