Cope if running in a non-browser environment and these vars don't exist.

In lieu of factoring all browser bits out of js.Lib, this gets things working in environments like
nodeJS without users having to patch the standard library.

std/js/Lib.hx

@@ -47,8 +47,10 @@ class Lib {
 	}
 
 	static function __init__() untyped {
-		document = untyped __js__("document");
-		window = untyped __js__("window");
+		if( __js__("typeof document") != "undefined" )
+			document = __js__("document");
+		if( __js__("typeof window") != "undefined" )
+			window = __js__("window");
 		#if debug
 __js__('onerror = function(msg,url,line) {
 		var stack = $s.copy();