[gtk/picture-nullable-setters] picture: Make setters actually take NULL

[Matthias Clasen <matthiasc src gnome org>]

commit 8f4b0cd30dbcae5ac9d525055fa9c5b2655fbe07
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed May 26 07:30:09 2021 -0400

    picture: Make setters actually take NULL
    
    gtk_picture_set_file was claiming to be nullable,
    but choked on NULL.
    
    Fixes: #3974

 gtk/gtkpicture.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)
---
diff --git a/gtk/gtkpicture.c b/gtk/gtkpicture.c
index c6f82be0c0..194d2fc98a 100644
--- a/gtk/gtkpicture.c
+++ b/gtk/gtkpicture.c
@@ -586,7 +586,11 @@ gtk_picture_set_file (GtkPicture *self,
   g_set_object (&self->file, file);
   g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_FILE]);
 
-  paintable = gdk_paintable_new_from_file_scaled (file, gtk_widget_get_scale_factor (GTK_WIDGET (self)));
+  if (file)
+    paintable = gdk_paintable_new_from_file_scaled (file, gtk_widget_get_scale_factor (GTK_WIDGET (self)));
+  else
+    paintable = NULL;
+
   gtk_picture_set_paintable (self, paintable);
   g_clear_object (&paintable);