[java-atk-wrapper] Fix null dereference

[Samuel Thibault <sthibaul src gnome org>]

commit b17e5039ef9282299289083b65a5d2223ba6f998
Author: Samuel Thibault <samuel thibault ens-lyon org>
Date:   Sun Jul 28 10:59:01 2019 +0200

    Fix null dereference

 wrapper/org/GNOME/Accessibility/AtkText.java | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/wrapper/org/GNOME/Accessibility/AtkText.java b/wrapper/org/GNOME/Accessibility/AtkText.java
index 2cc39b9..33da91b 100644
--- a/wrapper/org/GNOME/Accessibility/AtkText.java
+++ b/wrapper/org/GNOME/Accessibility/AtkText.java
@@ -118,6 +118,8 @@ public class AtkText {
                                if (part == -1)
                                        return null;
                                AccessibleTextSequence seq = acc_ext_text.getTextSequenceAt(part, offset);
+                               if (seq == null)
+                                       return null;
                                return new StringSequence(seq.text, seq.startIndex, seq.endIndex+1);
                        } else {
                                return private_get_text_at_offset(offset, boundary_type);