Fixing NullReferenceExcepction in renaming Node

When I have no selected node and I press F2 key, NullReferenceException appears in method RenameSelectedNode(). I added not null condition, it is working now. Debugged in VS2017.

mRemoteV1/UI/Controls/ConnectionTree/ConnectionTree.cs

@@ -295,8 +295,11 @@ namespace mRemoteNG.UI.Controls
 
         public void RenameSelectedNode()
         {
-            _allowEdit = true;
-            SelectedItem.BeginEdit();
+            if (SelectedItem != null)
+            {
+                _allowEdit = true;
+                SelectedItem.BeginEdit();
+            }
         }
 
         public void DeleteSelectedNode()
@@ -440,4 +443,4 @@ namespace mRemoteNG.UI.Controls
         }
         #endregion
     }
-}
+}