Guarantee slash in rename

[jojo2357]

Minimal fix to #2752

Summary of additions and changes

• Help prevent the user from renaming the command to an illegal or incomplete command name

How to test this pull request

\newcommand{\mycommand}{my command}

[jojo2357]

Well I am going to look into making a custom rename dialog, but that can be in a separate pr tbh since it won't be this easy and I think there are bigger fish to fry like #2722

[PHPirates]

What would be the advantage of having a custom rename dialog? Just UI?

[jojo2357]

well the big idea would be that it would give the user commandName instead of \commandName since it would have its own createDialog implementation that would set the label text correctly. Not much else in the way of functionality since this fix was added