ensure the same card appears after an undo

aqt/main.py

@@ -628,7 +628,10 @@ Debug info:\n%s""") % traceback.format_exc(), help="DeckErrors")
     ##########################################################################
 
     def onUndo(self):
-        self.col.undo()
+        cid = self.col.undo()
+        if cid:
+            card = self.col.getCard(cid)
+            self.reviewer.cardQueue.append(card)
         self.reset()
         self.maybeEnableUndo()
 

aqt/reviewer.py

@@ -52,6 +52,7 @@ class Reviewer(object):
         if self.cardQueue:
             # undone/edited cards to show
             c = self.cardQueue.pop()
+            c.startTimer()
             self.hadCardQueue = True
         else:
             if self.hadCardQueue: