[dconf-editor] Fix missing header in search.

[Arnaud B. <arnaudb src gnome org>]

commit c6e1a53d92ca3cdc8ec34304c1b7ad35304dd797
Author: Arnaud Bonatti <arnaud bonatti gmail com>
Date:   Fri Jan 4 22:56:03 2019 +0100

    Fix missing header in search.
    
    If the search is started from a key, the ReturnListBoxRow
    will have the same context_id, and the header is missing.

 editor/registry-list.vala | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/editor/registry-list.vala b/editor/registry-list.vala
index 90aab7e..1fbb2f1 100644
--- a/editor/registry-list.vala
+++ b/editor/registry-list.vala
@@ -1154,7 +1154,10 @@ private abstract class RegistryList : Grid, BrowsableView, AdaptativeWidget
         {
             KeyListBoxRow key_list_box_row = (KeyListBoxRow) (!) row_content;
             uint16 context_id = key_list_box_row.context_id;
-            if (((ClickableListBoxRow) before.get_child ()).context_id != context_id)
+            ClickableListBoxRow? before_content = (ClickableListBoxRow?) before.get_child ();
+            if (before_content == null)
+                assert_not_reached ();
+            if ((!) before_content is ReturnListBoxRow || ((!) before_content).context_id != context_id)
             {
                 if (key_list_box_row.has_schema)
                 {