Allow blank input lines for shell-pipe commands

[joelim-work]

• Fixes Script runs differently in lf and in zsh, also looking to improve the default delete command #1078

This change allows the user to input blank lines during shell-pipe (%) commands simply by pressing Enter. Below is an example script to test with:

cmd test %{{
    echo "doing something..."
    sleep 1

    echo "press enter to continue"
    read dummy

    echo "continue doing something..."
    sleep 1
    echo "done"
}}