OER: fix empty length decoding, no zero padding allowed

[Nicceboy]

There was a logic bug when parsing zero padding and there was no length.

That was a cause for null string in #272 instead of None.

But after consulting the standard again, I think zero padding is not allowed even in OER in this case and whole function can be removed. Zeros are allowed in long format.

[XAMPPRocky]

This now needs to be rebased to resolve conflicts.

[Nicceboy]

Rebased

[XAMPPRocky]

Thank you for your PR!