vfs_fruit: fix ftruncating resource fork

vfs_fruit: fix ftruncating resource fork

fruit_ftruncate_rsrc_adouble() is called to effectively ftruncate() the
._ AppleDouble file to the requested size.

The VFS function SMB_VFS_NEXT_FTRUNCATE() otoh would attempt to truncate
to fsp *stream* in any way the next VFS module seems fit. As we know
we're stacked with a streams module, the module will attempt to truncate
the stream. So we're not truncating the ._ file.

This went unnoticed as the AppleDouble file header contains the
authorative resource fork size that was updated correctly.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=13076

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>