Make Goodbye and Choice choices mutually exclusive

apps/openmw/mwdialogue/dialoguemanagerimp.cpp

@@ -430,11 +430,13 @@ namespace MWDialogue
     }
 
     void DialogueManager::addChoice (const std::string& text, int choice)
+    {
+        if (!mGoodbye)
         {
             mIsInChoice = true;
-
             mChoices.push_back(std::make_pair(text, choice));
         }
+    }
 
     const std::vector<std::pair<std::string, int> >& DialogueManager::getChoices()
     {
@@ -448,7 +450,7 @@ namespace MWDialogue
 
     void DialogueManager::goodbye()
     {
-        mIsInChoice = false;
+        if (!mIsInChoice)
             mGoodbye = true;
     }