REG [5.1.1-5.3.1] QFileDialog returns invalid path for SSL webDAV directories (not mounted on drive letters)

Steps to reproduce:

• Microsoft Sharepoint Server
• Mount directory in Explorer using the context menu "Add network location" on "Computer"(Win7) or "This PC" (Win8) (Note: Do not use "Map network drive")
• add network address like https://server/directory
• The directory is not mounted on a drive letter, but as a top level directory to the "Computer"-entry in explorer

Launch QFileDialog::getOpenFileNames and locate file from SSL webDAV directory (\\host@SSL\DavWWWRoot\directory\file.suffix) and check fileinfo. It returns correct info in Qt 5.1.1 but not anymore on later versions.

Qt 5.1.1
Path as QString: //host@SSL/DavWWWRoot/directory/VA20B/file.suffix
file path: //host@SSL/DavWWWRoot/directory/VA20B/file.suffix
absolute file path: //host@SSL/DavWWWRoot/directory/VA20B/file.suffix
canonical file path: //host@SSL/DavWWWRoot/directory/VA20B/file.suffix
QFileInfo exists: yes

Qt 5.3.1
Path as QString: /DavWWWRoot/directory/VA20B/file.suffix
file path: /DavWWWRoot/directory/VA20B/file.suffix
absolute file path: C:/DavWWWRoot/directory/VA20B/file.suffix
canonical file path:
QFileInfo exists: no

Regression is possible caused because of the change(s):

• f5dbc876378ae58a7bdfe1e9664fc81caca18dfb https://codereview.qt-project.org/#/c/56220/ Have QFileDialog use QUrl internally
• 5069e203d7aff7fb49bf746071f66bfd41c1ae89 https://codereview.qt-project.org/#/c/56221/ Add QUrl based API to QFileDialog

There's change to use QUrl::toLocalFile() instead of string which makes ssl web directory invalid to fileinfo.