We ask READ_EXTERNAL_STORAGE permission on first start
then check WRITE_EXTERNAL_STORAGE permission on switching
between document providers. This causes problems on Android 8+
Signed-off-by: Mert Tumer <merttumer@outlook.com>

Change-Id: Ia7290e33b2a55f5a2197374ca39c60998edfff72
Reviewed-on: https://gerrit.libreoffice.org/62269Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>
Tested-by: Jenkins