ASN1: rewrite _decode_der
ASN1: rewrite _decode_der

this rewrite makes phpseclib better able to handle indef lengths,
which had previously been untested.

kenichiii/phpseclib,thaigialai1987/phpseclib,danog/phpseclib,terrafrost/phpseclib,phpseclib/phpseclib,paragonie-scott/phpseclib,melya/phpseclib,kenichiii/phpseclib,metaclassing/phpseclib,thaigialai1987/phpseclib,danog/phpseclib,splitice/phpseclib,creatuity/phpseclib,splitice/phpseclib,melya/phpseclib,paragonie-scott/phpseclib,creatuity/phpseclib,metaclassing/phpseclib