[smuxi] Common: fixed build on .NET 3.5

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

commit a81df5501e29fd0457497b9ae8104d63dec9ceb6
Author: Mirco Bauer <meebey meebey net>
Date:   Wed Feb 4 15:18:53 2015 +0100

    Common: fixed build on .NET 3.5
    
    Path.Combine() with more than 2 arguments was added in .NET 4.0

 src/Common/IconCache.cs |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/src/Common/IconCache.cs b/src/Common/IconCache.cs
index 96f696b..b3196ee 100644
--- a/src/Common/IconCache.cs
+++ b/src/Common/IconCache.cs
@@ -54,7 +54,8 @@ namespace Smuxi.Common
         /// </remarks>
         public bool TryGetIcon(string protocol, string iconName, out string value)
         {
-            var iconPath = Path.Combine(f_IconsPath, protocol, iconName);
+            var iconPath = Path.Combine(f_IconsPath, protocol);
+            iconPath = Path.Combine(iconPath, iconName);
             var iconFile = new FileInfo(iconPath);
             if (iconFile.Exists && iconFile.Length > 0) {
                 value = iconPath;