[shotwell] Also set dark wallpaper uri

[Jens Georg <jensgeorg src gnome org>]

commit 0128e48c59291a4afb4580cbe588b05dea193c03
Author: Jens Georg <mail jensge org>
Date:   Mon Apr 4 21:58:55 2022 +0200

    Also set dark wallpaper uri
    
    Work-around non-working wallpaper in dark mode
    
    Fixes lp#1965812

 src/config/GSettingsEngine.vala | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/src/config/GSettingsEngine.vala b/src/config/GSettingsEngine.vala
index d19425e6..20527abd 100644
--- a/src/config/GSettingsEngine.vala
+++ b/src/config/GSettingsEngine.vala
@@ -369,6 +369,13 @@ public class GSettingsConfigurationEngine : ConfigurationEngine, GLib.Object {
             converted_val = "file://" + val;
         }
 
+        try {
+            if (p == ConfigurableProperty.DESKTOP_BACKGROUND_FILE) {
+                set_gs_string(schema_names[p], key_names[p] + "-dark", converted_val);
+            }
+        } catch (Error error) {
+            // Do nothing, the setting does not exist (yet)
+        }
         set_gs_string(schema_names[p], key_names[p], converted_val);
         property_changed(p);
     }