History has too many columns

While implementing the positional translation scheme, I stumbled upon the following issue:

If no flags are passed to SaQC we still end up with a pre-filled SaQC._flags-dios (every column is filled with -np.inf), the same is, of course, true for the respective flags.history. This turns out to be a problem in case of the positional flagging scheme. Here we explicitly evaluate the history of the flags to build up a flag, that consists of as many digits as we ran tests on the data (e.g. 2 tests should result in a flag like 902, with 0-> UNFLAGGED or GOOD and 2 -> BAD).

But with the current flags/history implementation we are always off-by-one: Even if we didn't call any test function at all, we still have a column in the history, if we called 2 tests, we have three history-columns (thus yielding flags like 9002).

(I guess,) I also can't just throw the first history columns away, as they might be user given and therefore actually relevant.