tdf#93634 repair getDisplayDirectory for Windows filepicker

Change wrong PROP_FILENAME to correct PROP_DIRECTORY

Change-Id: Iab2e16c486f487699e1574ed508539d95884bf9b
Reviewed-on: https://gerrit.libreoffice.org/18127Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>
(cherry picked from commit 8775593b)
Reviewed-on: https://gerrit.libreoffice.org/18373

fpicker/source/win32/filepicker/VistaFilePicker.cxx

@@ -246,7 +246,7 @@ OUString SAL_CALL VistaFilePicker::getDisplayDirectory()
     RequestRef rRequest(new Request());
     rRequest->setRequest (VistaFilePickerImpl::E_GET_DIRECTORY);
     m_aAsyncExecute.triggerRequestThreadAware(rRequest, AsyncRequests::BLOCKED);
-    const OUString sDirectory = rRequest->getArgumentOrDefault(PROP_FILENAME, OUString());
+    const OUString sDirectory = rRequest->getArgumentOrDefault(PROP_DIRECTORY, OUString());
 
     return sDirectory;
 }