REGRESSION (r167689): Hovering file name in a file input causes a crash

REGRESSION (r167689): Hovering file name in a file input causes a crash
https://bugs.webkit.org/show_bug.cgi?id=132214

Reviewed by Andreas Kling.

Source/WebCore:
The bug was caused by callDefaultEventHandlersInTheBubblingOrder unconditionally
accessing path.contextAt(0) even if the event path was empty.

Fixed the bug by exiting early when the event path is empty.

Test: fast/events/shadow-event-path-2.html

* dom/EventDispatcher.cpp:
(WebCore::callDefaultEventHandlersInTheBubblingOrder):

LayoutTests:
Add a regression test.

* fast/events/shadow-event-path-2-expected.txt: Added.
* fast/events/shadow-event-path-2.html: Added.
* fast/events/shadow-event-path.html:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167840 268f45cc-cd09-0410-ab3c-d52691b4dbfc