Option '--height' destroys results on stdout

- [x] I have read through the manual page (`man fzf`)
- [x] I have the latest version of fzf
- [x] I have searched through the existing issues

## Info

- OS
- [x] Linux
- [ ] Mac OS X
- [ ] Windows
- [ ] Etc.
- Shell
- [x] bash
- [ ] zsh
- [ ] fish

## Problem / Steps to reproduce

If running e.g. `fzf --height=30% --bind=alt-enter:"execute(echo TEST)"` and hitting `alt-enter`, the text `TEST` is **not** printed although the command seems to be executed (can be tested with e.g. `touch`).
It works without the option `--height`. It also works if stdout is piped to a file directly (`fzf [...] >/tmp/testfile`), but it does not work if piped through `cat` (`fzf [...] | cat`).