MDEV-31059 "Slave SQL" errors upon concurrent DML and erroneous ALTER

Skip more rpl-related error handling.
Also move the error check inside if (table) -- otherwise the error
should be handled already.

mysql-test/main/alter_table_online_debug.result

@@ -1364,6 +1364,7 @@ drop table t;
 set debug_sync= reset;
 disconnect con1;
 disconnect con2;
+NOT FOUND /Slave SQL/ in mysqld.1.err
 #
 # End of 11.2 tests
 #

mysql-test/main/alter_table_online_debug.test

@@ -1549,6 +1549,9 @@ drop table t;
 set debug_sync= reset;
 --disconnect con1
 --disconnect con2
+let SEARCH_FILE= $MYSQLTEST_VARDIR/log/mysqld.1.err;
+let SEARCH_PATTERN= Slave SQL;
+--source include/search_pattern_in_file.inc
 --echo #
 --echo # End of 11.2 tests
 --echo #

sql/log_event_server.cc

@@ -5218,26 +5218,29 @@ int Rows_log_event::do_apply_event(rpl_group_info *rgi)
       thd->clear_error(1);
       error= 0;
     }
-  } // if (table)
 
+    if (unlikely(error))
+    {
+      if (rpl_data.is_online_alter())
+        goto err;
+      slave_rows_error_report(ERROR_LEVEL, error, rgi, thd, table,
+                              get_type_str(),
+                              RPL_LOG_NAME, log_pos);
+      /*
+        @todo We should probably not call
+        reset_current_stmt_binlog_format_row() from here.
   
-  if (unlikely(error))
-  {
-    slave_rows_error_report(ERROR_LEVEL, error, rgi, thd, table,
-                             get_type_str(),
-                             RPL_LOG_NAME, log_pos);
-    /*
-      @todo We should probably not call
-      reset_current_stmt_binlog_format_row() from here.
+        Note: this applies to log_event_old.cc too.
+        /Sven
+      */
+      thd->reset_current_stmt_binlog_format_row();
+      thd->is_slave_error= 1;
+      /* remove trigger's tables */
+      goto err;
+    }
+  } // if (table)
 
-      Note: this applies to log_event_old.cc too.
-      /Sven
-    */
-    thd->reset_current_stmt_binlog_format_row();
-    thd->is_slave_error= 1;
-    /* remove trigger's tables */
-    goto err;
-  }
+  DBUG_ASSERT(error == 0);
 
   /*
     Remove trigger's tables. In case of ONLINE ALTER TABLE, event doesn't own