Processing of maliciously crafted length fields causes memory allocation SIGABRTs

Affected versions of this crate tried to preallocate a vector for an arbitrary amount of bytes announced by the ASN.1-DER length field without further checks.

This allows an attacker to trigger a SIGABRT by creating length fields that announce more bytes than the allocator can provide.

The flaw was corrected by not preallocating memory.