[gnome-photos] preview-view: Don't propagate motion-notify events after handling them

[Debarshi Ray <debarshir src gnome org>]

commit e7fc84ec46cc6c8e582d0b575f449887b22202f3
Author: Debarshi Ray <debarshir gnome org>
Date:   Thu Jun 15 12:04:11 2017 +0200

    preview-view: Don't propagate motion-notify events after handling them
    
    There is no immediate concern, but it makes sense to stop propagating
    the motion-notify event if it has been handled to scroll the item. This
    is also what PhotosToolCrop does.
    
    Fallout from b121e86bcdb1ba3bd55754e676b0c7a4cba9d116
    
    https://bugzilla.gnome.org/show_bug.cgi?id=742662

 src/photos-preview-view.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/src/photos-preview-view.c b/src/photos-preview-view.c
index 99ca67b..8b37a42 100644
--- a/src/photos-preview-view.c
+++ b/src/photos-preview-view.c
@@ -306,6 +306,7 @@ photos_preview_view_motion_notify_event (GtkWidget *widget, GdkEvent *event, gpo
           self->event_y_last = event->motion.y;
 
           photos_utils_scrolled_window_scroll (GTK_SCROLLED_WINDOW (current_view_container), delta_x, 
delta_y);
+          ret_val = GDK_EVENT_STOP;
         }
     }
   else