Don't use syncadaptors until they are ready

Fixes #2453

plugins/tiddlywiki/filesystem/filesystemadaptor.js

@@ -24,6 +24,11 @@ function FileSystemAdaptor(options) {
 	$tw.utils.createDirectory($tw.boot.wikiTiddlersPath);
 }
 
+FileSystemAdaptor.prototype.isReady = function() {
+	// The file system adaptor is always ready
+	return true;
+};
+
 FileSystemAdaptor.prototype.getTiddlerInfo = function(tiddler) {
 	return {};
 };