[chronojump] Fixed crash on session add since tags code

[Xavier de Blas <xaviblas src gnome org>]

commit b12c3a00fb74315d98c51aea688c6d791abb239f
Author: Xavier de Blas <xaviblas gmail com>
Date:   Mon Dec 7 13:28:10 2020 +0100

    Fixed crash on session add since tags code

 src/gui/app1/session/addEdit.cs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/src/gui/app1/session/addEdit.cs b/src/gui/app1/session/addEdit.cs
index 31b6fabc..79c9bc2e 100644
--- a/src/gui/app1/session/addEdit.cs
+++ b/src/gui/app1/session/addEdit.cs
@@ -693,7 +693,9 @@ public partial class ChronoJumpWindow
                                LogB.Information("app1sae_on_button_accept_clicked C");
 
                                //tags have not been added yet because there was no sessionID
-                               tagSessionSelect.SQLUpdateTransaction(currentSession.UniqueID);
+                               if(tagSessionSelect != null)
+                                       tagSessionSelect.SQLUpdateTransaction(currentSession.UniqueID);
+
                                LogB.Information("app1sae_on_button_accept_clicked C2");
                        } else
                        {