MDEV-37120 Improve timeout log message clarity for empty binlog state

Fixed error message confusion in semi-sync replication timeout logs.
When no previous successful semi-sync replication exists, the log
now shows "(none)" instead of displaying an empty filename.
Additionally, changed "semi-sync up to file" to "last semi-sync at file"
for better semantic accuracy.

All new code of the whole pull request, including one or several files
that are either new files or modified ones, are contributed under the
BSD-new license. I am contributing on behalf of my employer Amazon Web
Services, Inc.

Author: akshatnehra

sql/semisync_master.cc

@@ -964,7 +964,8 @@ int Repl_semi_sync_master::commit_trx(const char *trx_wait_binlog_name,
          * semi-sync was turned off then on, so on debug builds, we track
          * the number of times semi-sync turned off at binlogging, and compare
          * to the current value. */
-        DBUG_ASSERT(rpl_semi_sync_master_off_times > thd->expected_semi_sync_offs);
+        DBUG_ASSERT(rpl_semi_sync_master_off_times >
+                    thd->expected_semi_sync_offs);
 
         break;
       }
@@ -1033,10 +1034,11 @@ int Repl_semi_sync_master::commit_trx(const char *trx_wait_binlog_name,
       if (wait_result != 0)
       {
         /* This is a real wait timeout. */
-        sql_print_warning("Timeout waiting for reply of binlog (file: %s, pos: %lu), "
-                          "semi-sync up to file %s, position %lu.",
+        sql_print_warning("Timeout waiting for reply of binlog (file: %s, pos:"
+                          " %lu), last semi-sync at file %s, position %lu.",
                           trx_wait_binlog_name, (ulong)trx_wait_binlog_pos,
-                          m_reply_file_name, (ulong)m_reply_file_pos);
+                          (m_reply_file_name[0] == '\0') ? "(none)" :
+                           m_reply_file_name, (ulong)m_reply_file_pos);
         rpl_semi_sync_master_wait_timeouts++;
 
         /* switch semi-sync off */