Segfault: 'prepared_statement' test from 2.2 branch causes crash with 'develop'

steps to reproduce:

• install Maxscale from 'develop' branch
• run 'prepared_statement' test from 2.2 branch

Results:

Program terminated with signal 11, Segmentation fault.
#0 0x00007f779bee6148 in maxscale::Backend::server (this=0x1) at /home/vagrant/MaxScale/include/maxscale/backend.hh:140
140 /home/vagrant/MaxScale/include/maxscale/backend.hh: No such file or directory.
Missing separate debuginfos, use: debuginfo-install maxscale-2.3.4-1.x86_64
(gdb) bt
#0 0x00007f779bee6148 in maxscale::Backend::server (this=0x1) at /home/vagrant/MaxScale/include/maxscale/backend.hh:140
#1 0x00007f7790f63410 in RWSplitSession::handle_slave_is_target (this=0x7f778003cdc0, cmd=3 '\003', stmt_id=0)
at /home/vagrant/MaxScale/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc:895
#2 0x00007f7790f615bf in RWSplitSession::route_single_stmt (this=0x7f778003cdc0, querybuf=0x7f778003d2b0)
at /home/vagrant/MaxScale/server/modules/routing/readwritesplit/rwsplit_route_stmt.cc:260
#3 0x00007f7790f5642b in RWSplitSession::routeQuery (this=0x7f778003cdc0, querybuf=0x7f778003d2b0)
at /home/vagrant/MaxScale/server/modules/routing/readwritesplit/rwsplitsession.cc:174
#4 0x00007f7790f50dec in maxscale::Router<RWSplit, RWSplitSession>::routeQuery (pData=0x7f778003cdc8, pPacket=0x7f778003d2b0)
at /home/vagrant/MaxScale/include/maxscale/router.hh:449
#5 0x00007f779bfac403 in session_route_query (session=0x7f7774012080, buffer=0x7f778003d2b0) at /home/vagrant/MaxScale/server/core/session.cc:546
#6 0x00007f77913a2267 in route_by_statement (session=0x7f7774012080, capabilities=4295491975, p_readbuf=0x7f778aff8100)
at /home/vagrant/MaxScale/server/modules/protocol/MySQL/mariadbclient/mysql_client.cc:1746
#7 0x00007f77913a0d28 in gw_read_finish_processing (dcb=0x7f7774013e90, read_buffer=0x0, capabilities=4295491975)
at /home/vagrant/MaxScale/server/modules/protocol/MySQL/mariadbclient/mysql_client.cc:1203
#8 0x00007f77913a0b8e in gw_read_normal_data (dcb=0x7f7774013e90, read_buffer=0x7f778003d2b0, nbytes_read=32)
at /home/vagrant/MaxScale/server/modules/protocol/MySQL/mariadbclient/mysql_client.cc:1149
#9 0x00007f779139f0c8 in gw_read_client_event (dcb=0x7f7774013e90) at /home/vagrant/MaxScale/server/modules/protocol/MySQL/mariadbclient/mysql_client.cc:544
#10 0x00007f779bf262a8 in dcb_process_poll_events (dcb=0x7f7774013e90, events=5) at /home/vagrant/MaxScale/server/core/dcb.cc:2658
#11 0x00007f779bf26644 in dcb_handler (dcb=0x7f7774013e90, events=5) at /home/vagrant/MaxScale/server/core/dcb.cc:2743
#12 0x00007f779bf266ea in dcb_poll_handler (data=0x7f7774013e90, worker=0x1ee8f50, events=5) at /home/vagrant/MaxScale/server/core/dcb.cc:2779
#13 0x00007f779bfc9dd9 in maxbase::Worker::poll_waitevents (this=0x1ee8f50) at /home/vagrant/MaxScale/maxutils/maxbase/src/worker.cc:846
#14 0x00007f779bfc9023 in maxbase::Worker::run (this=0x1ee8f50, pSem=0x7ffce2f665e0) at /home/vagrant/MaxScale/maxutils/maxbase/src/worker.cc:545
#15 0x00007f779bfc97af in maxbase::Worker::thread_main (pThis=0x1ee8f50, pSem=0x7ffce2f665e0) at /home/vagrant/MaxScale/maxutils/maxbase/src/worker.cc:671
#16 0x00007f779bfcff7e in std::_Bind_simple<void ((maxbase::Worker, maxbase::Semaphore*))(maxbase::Worker*, maxbase::Semaphore*)>::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) (this=0x1f04d60) at /usr/include/c++/4.8.2/functional:1732
#17 0x00007f779bfcf795 in std::_Bind_simple<void ((maxbase::Worker, maxbase::Semaphore*))(maxbase::Worker*, maxbase::Semaphore*)>::operator()() (
this=0x1f04d60) at /usr/include/c++/4.8.2/functional:1720
#18 0x00007f779bfcf480 in std::thread::_Impl<std::_Bind_simple<void ((maxbase::Worker, maxbase::Semaphore*))(maxbase::Worker*, maxbase::Semaphore*)> >::_M_run() (this=0x1f04d48) at /usr/include/c++/4.8.2/thread:115
#19 0x00007f779a6b02b0 in ?? () from /lib64/libstdc++.so.6
#20 0x00007f779b675e25 in start_thread () from /lib64/libpthread.so.0
#21 0x00007f779965934d in clone () from /lib64/libc.so.6