[chronojump] Extra safety on genericWindow HideAndNull

[Xavier de Blas <xaviblas src gnome org>]

commit ecabd2d2ba8fdf9db77e4b6c5ff30c69b4a14a11
Author: Xavier de Blas <xaviblas gmail com>
Date:   Fri Oct 4 18:46:40 2019 +0200

    Extra safety on genericWindow HideAndNull

 src/gui/genericWindow.cs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/src/gui/genericWindow.cs b/src/gui/genericWindow.cs
index 9d30e5c4..b8a136f2 100644
--- a/src/gui/genericWindow.cs
+++ b/src/gui/genericWindow.cs
@@ -985,8 +985,12 @@ public class GenericWindow
        
        //when ! HideOnAccept, use this to close window
        //also is better to call it always tat is closed clicking on accept (after data has been readed)
-       public void HideAndNull() {
-               GenericWindowBox.generic_window.Hide();
+       public void HideAndNull()
+       {
+               //this check is extra safety if there are extra EventHandlers opened with +=
+               if(GenericWindowBox.generic_window != null)
+                       GenericWindowBox.generic_window.Hide();
+
                GenericWindowBox = null;
        }