Only show Dark/Light Theme bottom menu when on @isset ($codeMirror)

[samsonasik]

Avoid error undefined theme javascript error, as only when codeMirror is set.

[localhost:8000:56:22](http://localhost:8000/)
Uncaught TypeError: theme is null
    toggleTheme http://localhost:8000/:72
    onclick http://localhost:8000/:1

[samsonasik]

Fixed and deployed 👍

[TomasVotruba]

This should be available on any page, so people are not confused by disappearing option.

Independent on code mirror itself.

[samsonasik]

Then it seems variable id "theme-link" exists seems needed to avoid error:

[localhost:8000:56:22](http://localhost:8000/)
Uncaught TypeError: theme is null
    toggleTheme http://localhost:8000/:72
    onclick http://localhost:8000/:1

[samsonasik]

@TomasVotruba I created PR :

• Re-add Dark/Light Theme link #3007

to re-add it while avoid error Uncaught TypeError: theme is null