Clear opaque and transparent array in WebGLRenderer.dispose (#8987) (#9011)

src/renderers/WebGLRenderer.js

@@ -517,6 +517,11 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	this.dispose = function() {
 
+		transparentObjects = [];
+		transparentObjectsLastIndex = -1;
+		opaqueObjects = [];
+		opaqueObjectsLastIndex = -1;
+
 		_canvas.removeEventListener( 'webglcontextlost', onContextLost, false );
 
 	};