Tests whether expired/valid link share is still accessible.
Perform expiration date checking before returning share data for token.
Merge pull request #4856 from owncloud/fix-link-expiration

Fix Sharing "Expiration Date" for Shares of type Link (i.e. Token)

* owncloud/fix-link-expiration:
  Perform expiration date checking before returning share data for token.
  Tests whether expired/valid link share is still accessible.