Panic on incorrect date input to `simple_asn1`

Version 0.6.0 of the simple_asn1 crate panics on certain malformed
inputs to its parsing functions, including from_der and der_decode.
Because this crate is frequently used with inputs from the network, this
should be considered a security vulnerability.

The issue occurs when parsing the old ASN.1 “UTCTime” time format. If an
attacker provides a UTCTime where the first character is ASCII but the
second character is above 0x7f, a string slice operation in the
from_der_ function will try to slice into the middle of a UTF-8
character, and cause a panic.

This error was introduced in commit
d7d39d709577710e9dc8,
which updated simple_asn1 to use time instead of chrono because of
RUSTSEC-2020-159.
Versions of simple_asn1 before 0.6.0 are not affected by this issue.

The patch was applied in
simple_asn1 version 0.6.1.