[smuxi] Frontend: fixed leaking ChatViewSyncManager.Chats

[Mirco M. M. Bauer <mmmbauer src gnome org>]

commit dce4f7b57efb6ca82d63d740d2879bf1f9582c73
Author: Mirco Bauer <meebey meebey net>
Date:   Sun Jul 20 21:26:43 2014 +0200

    Frontend: fixed leaking ChatViewSyncManager.Chats

 src/Frontend/ChatViewSyncManager.cs |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/src/Frontend/ChatViewSyncManager.cs b/src/Frontend/ChatViewSyncManager.cs
index 3f5ef9a..8330b32 100644
--- a/src/Frontend/ChatViewSyncManager.cs
+++ b/src/Frontend/ChatViewSyncManager.cs
@@ -561,6 +561,10 @@ namespace Smuxi.Frontend
         public void Clear()
         {
             Trace.Call();
+
+            lock (Chats) {
+                Chats.Clear();
+            }
         }
 
         object GetChatKey(ChatModel chatModel)