Parser shouldn't allow account starting with semicolon

[tbm]

ledger is quite permissive in terms of what it accepts as account names - pretty much anything as long as it's followed by two spaces or a tab (or a newline). Account names may contain semicolons.

However, account names can't start with a semicolon... because that would be parsed as a comment instead. That makes sense.

Simple, right.

Except that ledger accepts an account name starting with a semicolon when you put a flag in front:

2018-01-02 * Account name starting with semicolon
    * ;A        10.00 EUR
    B

ledger -f c bal a
           10.00 EUR  ;A

This should be rejected.