QFileDialog/win: pass only filename to IFileDialog::SetFileName()

One more place were we should only pass the filename instead the full
path to IFileDialog::SetFileName()
Amends 19c701d370512e81d1b934f899b03ae0c2e6953f

Pick-to: 6.6
Task-number: QTBUG-47159
Change-Id: I3ac36eb2b6b6fe84fe6985590da882b1d5733efa
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit 2643210bd6e07aa1d8ae78c109592bdc2545b074)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/plugins/platforms/windows/qwindowsdialoghelpers.cpp

@@ -1551,7 +1551,7 @@ QWindowsNativeDialogBase *QWindowsFileDialogHelper::createNativeDialog()
             if (!info.isDir())
                 result->selectFile(info.fileName());
         } else {
-            result->selectFile(url.path()); // TODO url.fileName() once it exists
+            result->selectFile(url.fileName());
         }
     }
     // No need to select initialNameFilter if mode is Dir