Here-documents fail if the umask does not allow user reading.

$ zsh -c $'umask u-r; cat <<EOF\nEOF'
zsh:1: can't create temp file for here document: permission denied

Silly though 'umask u-r' may be, the fact that here-documents use
temporary files on zsh is an internal implementation detail that should
make no difference to the script. It is trivial to save and temporarily
fix the umask during the creation of the temporary file.

This may fix a few other things that use gettempfile() as well.

- M.