[gnome-photos] base-item: Assert that the output stream is a valid GFileOutputStream

[Debarshi Ray <debarshir src gnome org>]

commit 225d6ef9befcd8b87291c0b331819b1233dd53fc
Author: Debarshi Ray <debarshir gnome org>
Date:   Sun Feb 4 14:34:30 2018 +0100

    base-item: Assert that the output stream is a valid GFileOutputStream

 src/photos-base-item.c | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/src/photos-base-item.c b/src/photos-base-item.c
index 54b4ba35..bc78263e 100644
--- a/src/photos-base-item.c
+++ b/src/photos-base-item.c
@@ -2101,6 +2101,8 @@ photos_base_item_save_to_dir_file_create (GObject *source_object, GAsyncResult *
       goto out;
     }
 
+  g_assert_true (G_IS_FILE_OUTPUT_STREAM (stream));
+
   g_assert_null (data->unique_file);
   g_assert_true (G_IS_FILE (unique_file));
   data->unique_file = g_object_ref (unique_file);