[smuxi/stable] Engine: fix NRE in ChatModel.set_LastSeenHighlight and set_LastSeenMessage

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

commit 2b5e19bdbd03ced6b0849dfce4e0160835048db5
Author: Mirco Bauer <meebey meebey net>
Date:   Mon Mar 27 22:23:06 2017 +0800

    Engine: fix NRE in ChatModel.set_LastSeenHighlight and set_LastSeenMessage
    
    If a ChatModel is created but the MessageBuffer is not initialized yet, then
    ChatModel.set_LastSeenHighlight and also set_LastSeenMessage will throw a
    NullReferenceException like this:
    
        Server stack trace:
          at Smuxi.Engine.ChatModel.set_LastSeenHighlight (DateTime value) [0x00000] in 
/usr/local/src/smuxi-cloud/src/Engine/Chats/ChatModel.cs:136
          at (wrapper managed-to-native) System.Runtime.Remoting.RemotingServices:InternalExecute 
(System.Reflection.MethodBase,object,object[],object[]&)
          at System.Runtime.Remoting.RemotingServices.InternalExecuteMessage (System.MarshalByRefObject 
target, IMethodCallMessage reqMsg) [0x000c2] in 
/tmp/buildd/mono-2.10.8.1/mcs/class/corlib/System.Runtime.Remoting/RemotingServices.cs:138
    
        Exception rethrown at [0]:
          at (wrapper managed-to-native) System.Object:__icall_wrapper_mono_remoting_wrapper (intptr,intptr)
          at (wrapper remoting-invoke) Smuxi.Engine.ChatModel:set_LastSeenHighlight (System.DateTime)
          at (wrapper remoting-invoke-with-check) Smuxi.Engine.ChatModel:set_LastSeenHighlight 
(System.DateTime)
          at Smuxi.Frontend.Gnome.Notebook+<OnSwitchPage>c__AnonStorey0.<>m__0 () [0x00085] in 
/tmp/buildd/smuxi-1.0.6/src/Frontend-GNOME/Notebook.cs:264
    
    This is probably a race condition by an Engine that is creating and pushing a
    new chat to the frontend before the chat is fully initialized using
    ApplyConfig() or InitMessageBuffer(). Or the MessageBuffer had an error
    condition and got reset (to null) using ResetMessageBuffer().
    Thus this condition is now handled and logged for debugging purposes.

 src/Engine/Chats/ChatModel.cs |   26 ++++++++++++++++++++++++--
 1 files changed, 24 insertions(+), 2 deletions(-)
---
diff --git a/src/Engine/Chats/ChatModel.cs b/src/Engine/Chats/ChatModel.cs
index f62e7b7..0777fa6 100644
--- a/src/Engine/Chats/ChatModel.cs
+++ b/src/Engine/Chats/ChatModel.cs
@@ -133,7 +133,18 @@ namespace Smuxi.Engine
                 return MessageBuffer.LastSeenHighlight;
             }
             set {
-                MessageBuffer.LastSeenHighlight = value;
+                var msgBuffer = MessageBuffer;
+                if (msgBuffer == null) {
+#if LOG4NET
+                    _Logger.ErrorFormat(
+                        "{0}.set_LastSeenHighlight(): MessageBuffer is null, " +
+                        "ignoring set call...",
+                        this
+                    );
+#endif
+                    return;
+                }
+                msgBuffer.LastSeenHighlight = value;
             }
         }
 
@@ -145,7 +156,18 @@ namespace Smuxi.Engine
                 return MessageBuffer.LastSeenMessage;
             }
             set {
-                MessageBuffer.LastSeenMessage = value;
+                var msgBuffer = MessageBuffer;
+                if (msgBuffer == null) {
+#if LOG4NET
+                    _Logger.ErrorFormat(
+                        "{0}.set_LastSeenMessage(): MessageBuffer is null, " +
+                        "ignoring set call...",
+                        this
+                    );
+#endif
+                    return;
+                }
+                msgBuffer.LastSeenMessage = value;
             }
         }