[snap] Most shells not working

Hey, I wanted to give terminus a try but can't open a new terminal tab. The shell list is empty for me;
I tried to add zsh manually but couldn't figure out how to properly add it to the configuration file.

OS: Ubuntu 18.10
Shells: sh, bash, zsh
Default shell: zsh

Reproduce the empty shell list on Ubuntu 18.10 with sh, bash, and zsh, then trace the shell-list and configuration handling used when opening a new terminal tab. Done means the available shells populate and a new tab opens with the configured default shell, zsh.

Written by the indexing model from the issue text.