Make encoder-marc21 more forgiving?

[dr0i]

Came up in #527 :

If we parse (assumingly) crude binary MARC the encoding fails.
(first broken MRC seems to be 02589nas a2200601 c 4500 in https://raw.githubusercontent.com/gbv/Catmandu-Tutorial/master/data/marc.mrc (should be double checked with another MARC-validator other than MF:
Because MARCs binary directory of field 787 points to Iso646Constants.INFORMATION_SEPARATOR_2 = 0x1e the encoding breaks))

If an encoding breaks not only the field is dumped or the whole record but the whole stream. The dumping of the record and - more important- the whole stream can be avoided by piping decode-marc21 to catch-stream-exception before piping to encode-marc21.

a) if the record is indeed invalid:
aa) shall we make the encode-marc21 make more forgiving?
ab) or is it enough to bail out (as it is atm) resp. to expect the user to use catch-stream-exception resp. fix the invalid MARC ?
b) if the record is valid: fix encode-marc21