[gnome-photos] item-manager: Disallow setting arbitrary window modes while previewing

[Debarshi Ray <debarshir src gnome org>]

commit 8e03052527e205075aa6df84b9b744cb841fa6f4
Author: Debarshi Ray <debarshir gnome org>
Date:   Fri Oct 23 11:03:37 2015 +0200

    item-manager: Disallow setting arbitrary window modes while previewing
    
    The only thing you can do while in the preview is to go back.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=732799

 src/photos-item-manager.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/photos-item-manager.c b/src/photos-item-manager.c
index cf3570b..09d1226 100644
--- a/src/photos-item-manager.c
+++ b/src/photos-item-manager.c
@@ -753,6 +753,7 @@ photos_mode_controller_set_window_mode (PhotosModeController *self, PhotosWindow
 
   g_return_if_fail (mode != PHOTOS_WINDOW_MODE_NONE);
   g_return_if_fail (mode != PHOTOS_WINDOW_MODE_PREVIEW);
+  g_return_if_fail (self->mode != PHOTOS_WINDOW_MODE_PREVIEW);
 
   if (!photos_item_manager_set_window_mode_internal (self, mode, &old_mode))
     return;