`raise_unsupported_algorithm_impl()` peeked the OpenSSL error queue without
clearing it on the `ERR_R_UNSUPPORTED` and `ERR_R_FETCH_FAILED` branches,
so a later unrelated failure in the same thread reported the earlier error.

Clear the queue in those branches, and clear it in callers before the
OpenSSL operations whose failure is reported by that function or before
calling `get_asn1_utf8name_by_nid()`, which inspects the last error.