During InnoDB startup, change buffer merge operations are prohibited
before recv_apply_hashed_log_recs(true), which performs the last phase
of redo log apply. Before this call, ibuf_init_at_db_start() would be
invoked, and it could trigger the debug assertion.

ibuf_init_at_db_start(): Do not declare the mini-transaction as
"inside change buffer", because nothing is being written in the
mini-transaction. The purpose of this function is only to initialize
the memory data structures from the persistent data structures.