Fixed bug in ma_loghandler.cc that could cause an assert

The assert happens in 10.6 with the following command:

./mtr --no-reorder --verbose-restart main.update_ignore_216 main.upgrade_MDEV-19650 main.upgrade_MDEV-23102-1 main.upgrade_MDEV-23102-2 main.upgrade_geometrycolumn_procedure_definer main.upgrade_mdev_24363 main.varbinary sys_vars.aria_log_file_size_basic

Reviewer: Oleksandr Byelkin <sanja@mariadb.com>

storage/maria/ma_loghandler.c

@@ -7993,22 +7993,14 @@ void translog_flush_buffers(TRANSLOG_ADDRESS *lsn,
   }
   else
   {
-    if (log_descriptor.bc.buffer->last_lsn == LSN_IMPOSSIBLE)
+    if (log_descriptor.bc.buffer->last_lsn == LSN_IMPOSSIBLE &&
+        log_descriptor.bc.buffer->prev_last_lsn == LSN_IMPOSSIBLE)
     {
-      /*
-        In this case both last_lsn & prev_last_lsn are LSN_IMPOSSIBLE
-        otherwise it will go in the first IF because LSN_IMPOSSIBLE less
-        then any real LSN and cmp_translog_addr(*lsn,
-        log_descriptor.bc.buffer->prev_last_lsn) will be TRUE
-      */
-      DBUG_ASSERT(log_descriptor.bc.buffer->prev_last_lsn ==
-                  LSN_IMPOSSIBLE);
       DBUG_PRINT("info", ("There is no LSNs yet generated => do nothing"));
       translog_unlock();
       DBUG_VOID_RETURN;
     }
 
-    DBUG_ASSERT(log_descriptor.bc.buffer->prev_last_lsn != LSN_IMPOSSIBLE);
     /* fix lsn if it was horizon */
     *lsn= log_descriptor.bc.buffer->prev_last_lsn;
     DBUG_PRINT("info", ("LSN to flush fixed to prev last lsn: " LSN_FMT,