... to avoid treating \" as in-argument " instead of end of argument

See https://docs.microsoft.com/en-us/windows/desktop/api/shellapi/nf-shellapi-commandlinetoargvw

Change-Id: Ie283ba04117e13bc06c5b92412a945f945e67ff3
Reviewed-on: https://gerrit.libreoffice.org/61214
Tested-by: Jenkins
Reviewed-by: Mike Kaganski <mike.kaganski@collabora.com>