MDEV-34907 Bogus assertion failure and busy work while parsing FILE_ records

A server that was running with innodb_log_file_size=96M and
innodb_buffer_pool_size=6M had inserted some data into a table
that was subsequently dropped. When the server was killed and
restarted, an assertion failed in recv_sys_t::parse() while
a FSP_SIZE change was unnecessarily being processed during
the skip_the_rest: loop in recv_scan_log().

The ib_logfile0 contents was as follows:

1. The checkpoint start LSN points to the start of some mini-transaction.
2. There may be log records for modifying files for which a FILE_MODIFY
had been written before the checkpoint. These records were "purged"
by advancing the checkpoint.
3. At some point during the initial parsing with store=true the space
reserved for recv_sys.pages will run out and recv_scan_log() would switch
to the skip_the_rest: mode.
4. We encounter a log record for extending a tablespace that will be
deleted a bit later. This would trip the bogus debug assertion.
5. Later on, there would be a FILE_DELETE record for this tablespace.
6. The checkpoint end LSN points to a possibly empty sequence of
FILE_MODIFY records and a FILE_CHECKPOINT record. Recovery had parsed these
records first, before rewinding to the checkpoint start LSN.
7. There could be further records following the FILE_CHECKPOINT record.
Recovery will process all records until an inconsistency is found and
it is assumed that the end of the circular ib_logfile0 was reached.

recv_sys_t::parse(): For the template instantiation with store=false,
remove a debug assertion that could fail in a multi-batch recovery,
while recv_scan_log(false) would be in the skip_the_rest: loop.
It is very well possible that we have not encountered all FILE_ records
yet, and therefore we should not complain about unknown tablespaces.

Reviewed by: Debarun Banerjee

storage/innobase/log/log0recv.cc

@@ -2847,7 +2847,7 @@ recv_sys_t::parse_mtr_result recv_sys_t::parse(source &l, bool if_exists)
                                    last_offset)
                 : file_name_t::initial_flags;
               if (it == recv_spaces.end())
-                ut_ad(!file_checkpoint || space_id == TRX_SYS_SPACE ||
+                ut_ad(!store || space_id == TRX_SYS_SPACE ||
                       srv_is_undo_tablespace(space_id));
               else if (!it->second.space)
               {