Improve init function call-blocking error handling

[miloszm]

Summary

Currently, calling an init function via transaction throws error which has incorrect text.
It should say "init method call not allowed" rather than "Contract does not exist"

Possible solution design or implementation

The behaviour is caused by the following code:

            Error::ContractDoesNotExist(_) => Self::DoesNotExist,
            Error::InitalizationError(_) => Self::DoesNotExist,

Rather than DoesNotExist, some new constant should be used.

Additional context

The change requires double-checking to make sure that it does not influence state roots.