Unresponsive Web processes sometimes throw ObjC exceptions under didPerformActionMenu...

Unresponsive Web processes sometimes throw ObjC exceptions under didPerformActionMenuHitTest:
https://bugs.webkit.org/show_bug.cgi?id=140859
<rdar://problem/19571057>

Reviewed by Darin Adler.

* UIProcess/mac/WKImmediateActionController.mm:
(-[WKImmediateActionController didPerformActionMenuHitTest:userData:]):
If we've already given up on this gesture (either because it was canceled or the
willBeginAnimation timeout expired), we shouldn't build a new animationController for it.
This is true both because it wouldn't look good to swap animationControllers out
from under the gesture, but also because AppKit throws an exception when you do this
and that breaks a lot of things.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@179087 268f45cc-cd09-0410-ab3c-d52691b4dbfc