renderer: Disconnect theme change signal handler

The renderer does not stick around so we need to disconnect the signal
handler on "dispose". Since the renderer is not a GObject track the
signal id manually instead of using `g_signal_connect_object ()`.

Fixes 1995285 ("eek-renderer: Honor theme changes")

eek/eek-renderer.c

@@ -228,6 +228,8 @@ eek_renderer_free (EekRenderer        *self)
     g_object_unref(self->css_provider);
     g_object_unref(self->view_context);
     g_object_unref(self->button_context);
+    g_clear_signal_handler (&self->theme_name_id, gtk_settings_get_default());
+
     // this is where renderer-specific surfaces would be released
 
     free(self);
@@ -299,8 +301,8 @@ renderer_init (EekRenderer *self)
 
     gtk_settings = gtk_settings_get_default ();
 
-    g_signal_connect (gtk_settings, "notify::gtk-theme-name",
-                      G_CALLBACK (on_gtk_theme_name_changed), self);
+    self->theme_name_id = g_signal_connect (gtk_settings, "notify::gtk-theme-name",
+                                            G_CALLBACK (on_gtk_theme_name_changed), self);
 
     self->css_provider = squeek_load_style();
 }

eek/eek-renderer.h

@@ -39,6 +39,8 @@ typedef struct EekRenderer
     GtkStyleContext *button_context; // TODO: maybe move a copy to each button
     /// Style class for rendering the view and button CSS.
     gchar *extra_style; // owned
+    // Theme name change signal handler id
+    gulong theme_name_id;
 
     // Mutable state
     gint scale_factor; /* the outputs scale factor */