Try workaround für #758 (#914)

Try to work around the crash caused by an IllegalStateException by always returning a valid group view. Some change in Android seems to cause this. We'll keep this workaround until we've removed the `ExpandableListView`for good.

opentasks/src/main/java/org/dmfs/tasks/utils/ExpandableGroupDescriptorAdapter.java

@@ -112,6 +112,22 @@ public boolean hasStableIds()
     }
 
 
+    @Override
+    public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent)
+    {
+        try
+        {
+            return super.getGroupView(groupPosition, isExpanded, convertView, parent);
+        }
+        catch (IllegalStateException e)
+        {
+            // try to silence an issue which appears to be a race condition until we've gotten rid of ExpandableListView
+            // for now we just return an empty group view
+            return newGroupView(mContext, null /* we don't use this */, false, parent);
+        }
+    }
+
+
     @Override
     public void onLoadFinished(Loader<Cursor> loader, Cursor cursor)
     {