WireframeGeometry: Fixed addGroups() call. Fixes #7200.

src/extras/geometries/WireframeGeometry.js

@@ -81,7 +81,7 @@ THREE.WireframeGeometry = function ( geometry ) {
 
 			if ( drawcalls.length === 0 ) {
 
-				geometry.addDrawCall( 0, indices.length );
+				geometry.addGroup( 0, indices.length );
 
 			}