QFileDialog: reduce number of times a file is stat'ed

When opening a QFileDialog with an initial directory that lives on a
disconnected network drive, repeatedly testing that directory consumes
a significant amount of time during which the UI is blocked.

To reduce the amount of file accesses, refactor the initialization code
to allow sharing of a QFileInfo for the default case of operating on a
local and absolute file system. This reduces the amount of stat calls
significantly during startup time, and in case of a disconnected
network shaves of 10-15 seconds of blocked UI, if Windows has already
noticed that the file system is disconnected.

Pick-to: 5.15
Fixes: QTBUG-6039
Change-Id: Ie082e447db214033291455bef2087cd05f366806
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

0 files changed, 0 insertions, 0 deletions