[smuxi] Frontend-GNOME: fixed ArgumentNullException on .NET

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

commit 864aa3e54a364451452e2194742b09761ffa6962
Author: Mirco Bauer <meebey meebey net>
Date:   Tue Apr 28 20:57:55 2015 +0200

    Frontend-GNOME: fixed ArgumentNullException on .NET
    
    Fixed regression introduced in remember last seen highlight of commit
    3f72df04981847d4b4cd6380eaa26fd4ec916935. The .NET framework throws an
    ArgumentNullException if a Version is null and is compared in op_LessThan()

 src/Frontend-GNOME/Views/Chats/ChatView.cs |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/Frontend-GNOME/Views/Chats/ChatView.cs b/src/Frontend-GNOME/Views/Chats/ChatView.cs
index 5804307..0c53fb3 100644
--- a/src/Frontend-GNOME/Views/Chats/ChatView.cs
+++ b/src/Frontend-GNOME/Views/Chats/ChatView.cs
@@ -589,7 +589,8 @@ namespace Smuxi.Frontend.Gnome
         {
             _OutputMessageTextView.UpdateMarkerline();
             
-            if (Frontend.EngineProtocolVersion < new Version(0, 12)) {
+            if (Frontend.EngineProtocolVersion == null |
+                Frontend.EngineProtocolVersion < new Version(0, 12)) {
                 return;
             }