[java-atk-wrapper] Detect summary getting destroy while using it

[Samuel Thibault <sthibaul src gnome org>]

commit df0f61c3e80e5b67ee897df10bb3a9fea46a77f6
Author: Samuel Thibault <samuel thibault ens-lyon org>
Date:   Wed Jul 10 23:40:28 2019 +0200

    Detect summary getting destroy while using it

 jni/src/jawtable.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/jni/src/jawtable.c b/jni/src/jawtable.c
index f08e87d..96a2070 100644
--- a/jni/src/jawtable.c
+++ b/jni/src/jawtable.c
@@ -681,6 +681,8 @@ jaw_table_set_summary(AtkTable *table, AtkObject *summary)
   if ( !((*env)->IsInstanceOf(env, jsummary->acc_context, accessible)) )
     return;
   jobject obj = (*env)->NewGlobalRef(env, jsummary->acc_context);
+  if (!obj)
+    return;
   jobject atk_table = (*env)->NewGlobalRef(env, data->atk_table);
   if (!atk_table) {
     (*env)->DeleteGlobalRef(env, obj);