[Safari] Fix deselection of items in multiple selection

Steps to Reproduce:

• Navigate to a folder containing several documents.
• Select most of the documents.
• Start deselecting some of the documents.
  => Deselection is not always possible.

More specifically:
=> Cannot deselect at all with version 11.1 (11605.1.33.1.4)
=> Deselect sometimes takes several attempts with version 11.1 (13605.1.33.1.4), as seen in attached screencast.