[gnome-shell] screenShield: fix empty screen shield

[Lionel Landwerlin <llandwerlin src gnome org>]

commit 7403545a481e1a8e267d094673cdbe37229f629a
Author: Lionel Landwerlin <llandwerlin gmail com>
Date:   Wed Jun 26 14:47:33 2013 +0100

    screenShield: fix empty screen shield
    
    If the drag action ends after something else has put the screen shield
    into a different state we can end up in an inconsistent screen shield
    state where the whole thing is empty.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=703126

 js/ui/screenShield.js |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)
---
diff --git a/js/ui/screenShield.js b/js/ui/screenShield.js
index 254bc68..15cc65f 100644
--- a/js/ui/screenShield.js
+++ b/js/ui/screenShield.js
@@ -720,6 +720,8 @@ const ScreenShield = new Lang.Class({
     },
 
     _onDragEnd: function(action, actor, eventX, eventY, modifiers) {
+        if (this._lockScreenState != MessageTray.State.HIDING)
+            return;
         if (this._lockScreenGroup.y < -(ARROW_DRAG_THRESHOLD * global.stage.height)) {
             // Complete motion automatically
            let [velocity, velocityX, velocityY] = this._dragAction.get_velocity(0);