Fix: Avoid globals starting with 'i/'

[StraToN]

Fixes godot-escoria/escoria-issues#153

[BHSDuncan]

More of me being pedantic. :)

[dploeger]

@StraToN I'm confused. Wouldn't it make more sense to check in inventory_add whether the given global_Id doesn't have a "/" in its name?

[StraToN]

@dploeger That would also make sense but in this PR I wanted above all to forbid a global having 2 / characters in its name. Since inventory_add calls set_global, I intended to catch all cases there.

[dploeger]

Shouldn't have a global no / in the name at all? Even i/ is only a hack to work with inventory items. 🤔

[StraToN]

We could indeed modify the global manager to separate globals from inventory globals instead. Technically, nothing blocks the use of / characters in globals. And I'm just thinking that could actually be useful to keep, so that gamedevs can kind of "classify" their globals.

Which would advocate for a change in inventory_add instead as you mentioned.

I'll change that tomorrow morning.