fix crash on shutdown when duplicate mail db listeners have been registered r=naving, sr=sspitzer 141028

mailnews/db/msgdb/src/nsMsgDatabase.cpp

@@ -440,28 +440,32 @@ nsMsgDatabase::CreateMsgHdr(nsIMdbRow* hdrRow, nsMsgKey key, nsIMsgDBHdr* *resul
 
 NS_IMETHODIMP nsMsgDatabase::AddListener(nsIDBChangeListener *listener)
 {
-    if (m_ChangeListeners == nsnull) 
-	{
-        m_ChangeListeners = new nsVoidArray();
-        if (!m_ChangeListeners) 
-			return NS_ERROR_OUT_OF_MEMORY;
-    }
-	return m_ChangeListeners->AppendElement(listener);
+  if (m_ChangeListeners == nsnull) 
+  {
+    m_ChangeListeners = new nsVoidArray();
+    if (!m_ChangeListeners) 
+      return NS_ERROR_OUT_OF_MEMORY;
+  }
+  // check if this listener is already registered
+  // if already registered, do nothing (not an error)
+  else if (m_ChangeListeners->IndexOf(listener) != -1)
+    return NS_OK;
+  return m_ChangeListeners->AppendElement(listener);
 }
 
 NS_IMETHODIMP nsMsgDatabase::RemoveListener(nsIDBChangeListener *listener)
 {
-    if (m_ChangeListeners == nsnull) 
-		return NS_OK;
-	for (PRInt32 i = 0; i < m_ChangeListeners->Count(); i++)
-	{
-		if ((nsIDBChangeListener *) m_ChangeListeners->ElementAt(i) == listener)
-		{
-			m_ChangeListeners->RemoveElementAt(i);
-			return NS_OK;
-		}
-	}
-	return NS_COMFALSE;
+  if (m_ChangeListeners == nsnull) 
+    return NS_OK;
+  for (PRInt32 i = 0; i < m_ChangeListeners->Count(); i++)
+  {
+    if ((nsIDBChangeListener *) m_ChangeListeners->ElementAt(i) == listener)
+    {
+      m_ChangeListeners->RemoveElementAt(i);
+      return NS_OK;
+    }
+  }
+  return NS_COMFALSE;
 }
 
 	// change announcer methods - just broadcast to all listeners.
@@ -556,20 +560,20 @@ NS_IMETHODIMP nsMsgDatabase::NotifyParentChangedAll(nsMsgKey keyReparented, nsMs
 
 NS_IMETHODIMP nsMsgDatabase::NotifyAnnouncerGoingAway(void)
 {
-    if (m_ChangeListeners == nsnull)
-		return NS_OK;
-	// run loop backwards because listeners remove themselves from the list 
-	// on this notification
-	for (PRInt32 i = m_ChangeListeners->Count() - 1; i >= 0 ; i--)
-	{
-		nsIDBChangeListener *changeListener =
-            (nsIDBChangeListener *) m_ChangeListeners->ElementAt(i);
-
-		nsresult rv = changeListener->OnAnnouncerGoingAway(this); 
-        if (NS_FAILED(rv)) 
-			return rv;
-	}
+  if (m_ChangeListeners == nsnull)
     return NS_OK;
+  // run loop backwards because listeners remove themselves from the list 
+  // on this notification
+  for (PRInt32 i = m_ChangeListeners->Count() - 1; i >= 0 ; i--)
+  {
+    nsIDBChangeListener *changeListener =
+      (nsIDBChangeListener *) m_ChangeListeners->ElementAt(i);
+    
+    nsresult rv = changeListener->OnAnnouncerGoingAway(this); 
+    if (NS_FAILED(rv)) 
+      return rv;
+  }
+  return NS_OK;
 }
 
 
@@ -1070,6 +1074,11 @@ NS_IMETHODIMP nsMsgDatabase::ForceClosed()
     m_mdbStore->Release();
     m_mdbStore = nsnull;
   }
+  if (m_ChangeListeners) 
+  {
+    // better not be any listeners, because we're going away.
+    NS_ASSERTION(m_ChangeListeners->Count() == 0, "shouldn't have any listeners left");
+  }
   Release();
   return err;
 }