[java-atk-wrapper] Action: Fix crash on bogus index

[Samuel Thibault <sthibaul src gnome org>]

commit d48ac75b8ddc91389b13140e47510a2510c814da
Author: Samuel Thibault <samuel thibault ens-lyon org>
Date:   Sun Jul 28 11:37:52 2019 +0200

    Action: Fix crash on bogus index

 jni/src/jawaction.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)
---
diff --git a/jni/src/jawaction.c b/jni/src/jawaction.c
index 3903f81..abad372 100644
--- a/jni/src/jawaction.c
+++ b/jni/src/jawaction.c
@@ -204,12 +204,16 @@ jaw_action_get_description (AtkAction *action, gint i)
                                      data->jstrActionDescription,
                                      data->action_description);
     (*jniEnv)->DeleteGlobalRef(jniEnv, data->jstrActionDescription);
+    data->jstrActionDescription = NULL;
+    data->action_description = NULL;
   }
 
-  data->jstrActionDescription = (*jniEnv)->NewGlobalRef(jniEnv, jstr);
-  data->action_description = (gchar*)(*jniEnv)->GetStringUTFChars(jniEnv,
-                                                                  data->jstrActionDescription,
-                                                                  NULL);
+  if (jstr) {
+    data->jstrActionDescription = (*jniEnv)->NewGlobalRef(jniEnv, jstr);
+    data->action_description = (gchar*)(*jniEnv)->GetStringUTFChars(jniEnv,
+                                                                    data->jstrActionDescription,
+                                                                    NULL);
+  }
 
   return data->action_description;
 }