MDEV-19376 Repl_semi_sync_master::commit_trx assertion failure: ... || !m_active_tranxs->is_tranx_end_pos(trx_wait_binlog_name, trx_wait_binlog_pos)

The assert indicates that the current transaction got caught uncleaned from
the semisync master's cache when it is signaled to proceed upon its
ack receive.

The reason of missed cleanup turns out to be a flaw in the gtid
connect mode.
A submitted by connecting slave value of its last received event's
binlog file *name* was adopted into
{{Repl_semi_sync_master::m_reply_file_name}} as a part of semisync
initialization.

Notice that the initialization still refines the position part of the
submitted last received event's binlog coordinates.
The master side binlog filename:pos refinement is
specific to the gtid connect mode for purpose of computing the latest
binlog file to resume slave feeding from.
Effectively in the gtid connect mode the computed resumption filename:pos
may appear smaller in which case a new post-connect time committing
transaction may be logged with its filename:pos also less than the
submitted coordinates and that triggers the assert.

Fixed with making the semisync initialization to use the refined filename:pos.
It is guaranteed to be less than any new generated transaction's binlog:pos.

sql/sql_repl.cc

@@ -2725,7 +2725,11 @@ void mysql_binlog_send(THD* thd, char* log_ident, my_off_t pos,
      run hook first when all check has been made that slave seems to
      be requesting a reasonable position. i.e when transmit actually starts
   */
-  if (RUN_HOOK(binlog_transmit, transmit_start, (thd, flags, log_ident, pos)))
+
+  DBUG_ASSERT(pos == linfo.pos);
+
+  if (RUN_HOOK(binlog_transmit, transmit_start,
+               (thd, flags, linfo.log_file_name, linfo.pos)))
   {
     info->errmsg= "Failed to run hook 'transmit_start'";
     info->error= ER_UNKNOWN_ERROR;