In recv_sys_t::apply(), we were unnecessarily looking up pages
in buf_pool.page_hash and potentially waiting for exclusive page latches.

Before buf_page_get_low() would return an x-latched page,
that page will have to be read and buf_page_read_complete() would
have invoked recv_recover_page() to apply the log to the page.

Therefore, it suffices to invoke recv_read_in_area() to trigger
a transition from RECV_NOT_PROCESSED.

recv_read_in_area(): Take the iterator as a parameter, and remove
page_id lookups. Should the page already be in buf_pool.page_hash,
buf_page_init_for_read() will return nullptr to buf_read_page_low()
and buf_read_page_background().

recv_sys_t::apply(): Replace goto, remove dead code, and add assertions
to guarantee that the iteration will make progress.

Reviewed by: Vladislav Lesin