recv_log_format_0_recover(): Invoke log_decrypt_after_read() after
reading the old-format redo log buffer.

With this change, we will upgrade to an encrypted redo log that
is misleadingly carrying a MySQL 5.7.9 compatible format tag while
the log blocks (other than the header and the checkpoint blocks)
are in an incompatible, encrypted format.
That needs to be fixed by introducing a new redo log format tag that
indicates that the entire redo log is encrypted.