[gnome-shell/wip/carlosg/dnd-fixes: 13/14] dnd: Make startDrag() fail if there is a current grab

[Carlos Garnacho <carlosg src gnome org>]

commit 9b20ef584a87376574eac08a71230e1ec9b5daa2
Author: Carlos Garnacho <carlosg gnome org>
Date:   Tue Mar 12 01:53:16 2019 +0100

    dnd: Make startDrag() fail if there is a current grab
    
    This call just went through stomping over previous drag operations if any,
    _maybeStartDrag() accounted for this, but other callers (well, WindowClone
    in workspace.js) don't. This must bail out early even if a drag operation is
    requested, luckily all callers account for it already.
    
    This broke shell state by preserving connected captured-event handlers if
    one tried to drag multiple windows simultaneously through multitouch. We
    of course don't support that, now more elegantly.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/455

 js/ui/dnd.js | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/js/ui/dnd.js b/js/ui/dnd.js
index 614ea621d..929ee0e22 100644
--- a/js/ui/dnd.js
+++ b/js/ui/dnd.js
@@ -306,6 +306,9 @@ var _Draggable = class _Draggable {
      * for the draggable.
      */
     startDrag(stageX, stageY, time, sequence, device) {
+        if (currentDraggable)
+            return;
+
         if (device == undefined) {
             let event = Clutter.get_current_event();