Fixed webkit crash after selecting cancel button of authentication popup.

Fixed webkit crash after selecting cancel button of authentication popup.

When the authentication popup is displayed and user select the cancel (or ok),
webkit is terminated because cancel function is called twice by wrong deleted data reference.

[Title] Fixed webkit crash after authentication popup
[Issue#] N/A
[Problem] When the authentication popup is displayed and user select the cancel, webkit is terminated.
[Cause] authChallenge data is deleted after calling cancel and webkit is refer to deleted data and wrong operation is occurred.
[Solution] Change the timing of deleting authChallenge data to destruct ewkViewImple or handle another auth message.
[SCMRequest] N/A

Change-Id: Ie225218d9e07c308298610a64de50aad6e1a9c1a