LineSegments2: Fix typo in raycast (#21760)

* fix typo in LineSegments2 raycast

* don't modify class in examples/js

Co-authored-by: Amos <[email protected]>

examples/jsm/lines/LineSegments2.js

@@ -184,8 +184,8 @@ class LineSegments2 extends Mesh {
 			_start4.fromBufferAttribute( instanceStart, i );
 			_end4.fromBufferAttribute( instanceEnd, i );
 
-			_start.w = 1;
-			_end.w = 1;
+			_start4.w = 1;
+			_end4.w = 1;
 
 			// camera space
 			_start4.applyMatrix4( _mvMatrix );