[java-atk-wrapper] Fix null dereference

[Samuel Thibault <sthibaul src gnome org>]

commit fb59461739f8d7a1875e124c7c8da914e0eeedd6
Author: Samuel Thibault <samuel thibault ens-lyon org>
Date:   Sun Jul 28 00:29:49 2019 +0200

    Fix null dereference

 wrapper/org/GNOME/Accessibility/AtkSelection.java | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/wrapper/org/GNOME/Accessibility/AtkSelection.java 
b/wrapper/org/GNOME/Accessibility/AtkSelection.java
index bd4844c..f5840bc 100644
--- a/wrapper/org/GNOME/Accessibility/AtkSelection.java
+++ b/wrapper/org/GNOME/Accessibility/AtkSelection.java
@@ -62,7 +62,12 @@ public class AtkSelection {
                if (acc_selection == null)
                        return null;
 
-               return AtkUtil.invokeInSwing ( () -> { return 
acc_selection.getAccessibleSelection(i).getAccessibleContext(); }, null);
+               return AtkUtil.invokeInSwing ( () -> {
+                       Accessible sel = acc_selection.getAccessibleSelection(i);
+                       if (sel == null)
+                               return null;
+                       return sel.getAccessibleContext();
+               }, null);
        }
 
        public int get_selection_count () {