Fixed ROTATE_EVENT

If timestamp is zero and flag LOG_EVEBNT_ARTIFICIAL_F was set the
event is a fake ROTATE_EVENT (https://mariadb.com/kb/en/fake-rotate_event/)
and needs different handling:
- a checksum might follow if @@binlog_checksum was set (CRC32)
- length calculation is different

include/mariadb_rpl.h

@@ -155,6 +155,7 @@ typedef struct st_mariadb_rpl {
   uint32_t flags;
   uint8_t fd_header_len; /* header len from last format description event */
   uint8_t use_checksum;
+  uint8_t artificial_checksun;
 } MARIADB_RPL;
 
 /* Event header */