empty ee folder causes `Can't resolve ee_else_ce` error
Running CE, create empty `ee/` folder. I sometimes have leftover `ee/spec` folders if running tests when changing branches from EE to CE
Webpack build fails and prints errors
e.g.
```
11:42:16 webpack.1 | ERROR in ./main.js
11:42:16 webpack.1 | Module not found: Error: Can't resolve 'ee_else_ce/main_ee' i
```
## Possible solutions
a) add a more thorough check to [is_ee_env](https://gitlab.com/gitlab-org/gitlab-ee/blob/796624edb282cd47a232a12d7dd1a501bf1cfc62/config/helpers/is_ee_env.js#L9 )
b) print a warning
c) `rm ee/`
issue