If a CT log entry in CTLOG_FILE is invalid, skip it and continue loading

Previously, the remaining CT log entries would not be loaded.
Also, CTLOG_STORE_load_file would return 1 even if a log entry was
invalid, resulting in no errors being shown.

Reviewed-by: Ben Laurie <ben@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>