Fix for issue #309

Author: lachezar

jquery.pjax.js

@@ -403,7 +403,7 @@ function onPjaxPopstate(event) {
 
     // If popping back to the same state, just skip.
     // Could be clicking back from hashchange rather than a pushState.
-    if (pjax.state.id === state.id) return
+    if (pjax.state && pjax.state.id === state.id) return
 
     var container = $(state.container)
     if (container.length) {