The shift would overflow the value which could produce garbage output
that might get interpreted as real OIDs (in case strings are compared).
This limit allows OID sub-identifiers to consist of at most 4 bytes,
which should be enough for any real-world OIDs (it's also the maximum we
used in tests so far).
Fixes: f813069e89 ("fixed asn1_oid_to_string() conversion")
Tobias Brunner
502fa14536