[longomatch] Fix hiding of button properties when no button is selected.

[Andoni Morales Alastruey <amorales src gnome org>]

commit 841c4557405064aee132d2d40fcae5591554e9a8
Author: Xavi Artigas <xartigas fluendo com>
Date:   Tue Apr 14 11:10:37 2015 +0200

    Fix hiding of button properties when no button is selected.

 LongoMatch.Drawing/Widgets/DashboardCanvas.cs |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/LongoMatch.Drawing/Widgets/DashboardCanvas.cs b/LongoMatch.Drawing/Widgets/DashboardCanvas.cs
index caf595e..8d9e1f6 100644
--- a/LongoMatch.Drawing/Widgets/DashboardCanvas.cs
+++ b/LongoMatch.Drawing/Widgets/DashboardCanvas.cs
@@ -252,6 +252,9 @@ namespace LongoMatch.Drawing.Widgets
                protected override void SelectionChanged (List<Selection> sel)
                {
                        if (sel.Count == 0) {
+                               if (ButtonsSelectedEvent != null) {
+                                       ButtonsSelectedEvent (new List<DashboardButton> ());
+                               }
                                return;
                        }