[empathy] Only call SetChatState if the Channel supports it

[Will Thompson <wjt src gnome org>]

commit b15c53e7e8b21fcfb4e6c43e0740866a6c2a5130
Author: Will Thompson <will thompson collabora co uk>
Date:   Thu Aug 13 12:10:01 2009 +0100

    Only call SetChatState if the Channel supports it
    
    I'm sick of seeing spurious debug messages about this whenever I type
    anything into an IRC channel.

 libempathy/empathy-tp-chat.c |   17 ++++++++++-------
 1 files changed, 10 insertions(+), 7 deletions(-)
---
diff --git a/libempathy/empathy-tp-chat.c b/libempathy/empathy-tp-chat.c
index a328281..9300364 100644
--- a/libempathy/empathy-tp-chat.c
+++ b/libempathy/empathy-tp-chat.c
@@ -1328,13 +1328,16 @@ empathy_tp_chat_set_state (EmpathyTpChat      *chat,
 	g_return_if_fail (EMPATHY_IS_TP_CHAT (chat));
 	g_return_if_fail (priv->ready);
 
-	DEBUG ("Set state: %d", state);
-	tp_cli_channel_interface_chat_state_call_set_chat_state (priv->channel, -1,
-								 state,
-								 tp_chat_async_cb,
-								 "setting chat state",
-								 NULL,
-								 G_OBJECT (chat));
+	if (tp_proxy_has_interface_by_id (priv->channel,
+					  TP_IFACE_QUARK_CHANNEL_INTERFACE_CHAT_STATE)) {
+		DEBUG ("Set state: %d", state);
+		tp_cli_channel_interface_chat_state_call_set_chat_state (priv->channel, -1,
+									 state,
+									 tp_chat_async_cb,
+									 "setting chat state",
+									 NULL,
+									 G_OBJECT (chat));
+	}
 }