test_wl4435_3 case from mysql_client_test.c lead to crash

bt:

#0 0x00007fb6a62cf6ab in raise () from /lib64/libpthread.so.0
#1 0x00007fb6a1db9944 in log_unexpected_response (dcb=0x7fb6880249e0, buffer=0x7fb688026650)
at /home/xiangzhong.wxd/gitlab/MaxScale/server/modules/routing/readwritesplit/readwritesplit.cc:1155
#2 0x00007fb6a1db9bba in clientReply (instance=0x21b3940, router_session=0x7fb688024d50, writebuf=0x7fb688026650, backend_dcb=0x7fb6880249e0)
at /home/xiangzhong.wxd/gitlab/MaxScale/server/modules/routing/readwritesplit/readwritesplit.cc:1190
#3 0x00007fb6a131c974 in gw_read_and_write (dcb=0x7fb6880249e0) at /home/xiangzhong.wxd/gitlab/MaxScale/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.c:976
#4 0x00007fb6a131b581 in gw_read_backend_event (dcb=0x7fb6880249e0) at /home/xiangzhong.wxd/gitlab/MaxScale/server/modules/protocol/MySQL/mariadbbackend/mysql_backend.c:484
#5 0x00007fb6a67e2f55 in dcb_process_poll_events (dcb=0x7fb6880249e0, events=5) at /home/xiangzhong.wxd/gitlab/MaxScale/server/core/dcb.cc:3146

this case have SERVER_PS_OUT_PARAMS for stmt_exec