Internal Server Error because of CircleEntity.findByAlias

While browsing through the code, I've found this:

```Kotlin
@Transactional(readOnly = true)
open fun findByAlias(alias: String): CircleEntity {
return repo.findAllByAlias(alias)[0]
}
```

However, this might throw internal error: https://schpincer.sch.bme.hu/provider/langoscasdfh

I have not attempted to fix this, as much of the existing code could depend on it (haven't checked tho).

Start with CircleEntity.findByAlias and repo.findAllByAlias, then reproduce the failure at /provider/langoscasdfh and inspect the existing callers before deciding how the missing alias should be handled. Done means an invalid alias no longer produces an internal server error while existing callers continue to behave correctly.

Written by the indexing model from the issue text.