#9428: Fixed Lensflares with StereoEffect (#9880)

src/renderers/webgl/plugins/LensFlarePlugin.js

@@ -199,8 +199,8 @@ function LensFlarePlugin( renderer, flares ) {
 
 		var validArea = new Box2();
 
-		validArea.min.set( 0, 0 );
-		validArea.max.set( viewport.z - 16, viewport.w - 16 );
+		validArea.min.set( viewport.x, viewport.y );
+		validArea.max.set( viewport.x + ( viewport.z - 16 ), viewport.y + ( viewport.w - 16 ) );
 
 		if ( program === undefined ) {