fix 32bit index buffer extension not enable automatically when rendering Line

src/renderers/WebGLRenderer.js

@@ -1244,7 +1244,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 			var type, size;
 
-			if ( index.array instanceof Uint32Array ) {
+			if ( index.array instanceof Uint32Array && extensions.get( 'OES_element_index_uint' ) ) {
 
 				type = _gl.UNSIGNED_INT;
 				size = 4;