[empathy] Don't crash when switching to a tab with no TpChat

[Guillaume Desmottes <gdesmott src gnome org>]

commit 26024d8ad63511ec46f928d12bc2689098480104
Author: Will Thompson <will thompson collabora co uk>
Date:   Sat Feb 13 16:10:53 2010 +0000

    Don't crash when switching to a tab with no TpChat
    
    Fixes: #609843

 libempathy-gtk/empathy-chat.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/libempathy-gtk/empathy-chat.c b/libempathy-gtk/empathy-chat.c
index d27337b..5702adb 100644
--- a/libempathy-gtk/empathy-chat.c
+++ b/libempathy-gtk/empathy-chat.c
@@ -2947,8 +2947,12 @@ empathy_chat_messages_read (EmpathyChat *self)
 
 	g_return_if_fail (EMPATHY_IS_CHAT (self));
 
-	empathy_tp_chat_acknowledge_messages (priv->tp_chat,
+	if (priv->tp_chat != NULL) {
+		empathy_tp_chat_acknowledge_messages (priv->tp_chat,
 			priv->pending_messages);
+	}
+	/* ...else, we can't do any acknowledging because the channel (or
+	 * indeed connection) has gone away. */
 
 	while (priv->pending_messages != NULL) {
 		g_object_unref (priv->pending_messages->data);