Currently used file pickers API doesn't work for OS X < 10.6

Change-Id: I69592ada3a413cae2d0def2faa495db44894ed3f
Reviewed-on: https://gerrit.libreoffice.org/8430
Reviewed-by: Norbert Thiebaud <nthiebaud@gmail.com>
Tested-by: Norbert Thiebaud <nthiebaud@gmail.com>