WebGLRenderer: Fixed camera type check. See #9661.

src/renderers/WebGLRenderer.js

@@ -1126,7 +1126,7 @@ function WebGLRenderer( parameters ) {
 
 	this.render = function ( scene, camera, renderTarget, forceClear ) {
 
-		if ( ( camera && camera.isCamera ) === false ) {
+		if ( camera !== undefined && camera.isCamera !== true ) {
 
 			console.error( 'THREE.WebGLRenderer.render: camera is not an instance of THREE.Camera.' );
 			return;