Closing db with active live query causes crash

#0  0x0000000000000000 in ?? ()

#1  0x00007f143c77d0e2 in litecore::LiveQuerier::_runQuery (this=0x7f142801a3d0, options=...)

    at /home/couchbase/jenkins/workspace/couchbase-lite-c-debian9/couchbase-lite-c/vendor/couchbase-lite-core/LiteCore/Database/LiveQuerier.cc:192

#2  0x00007f143c77d731 in std::__invoke_impl<void, void (litecore::LiveQuerier::*&)(litecore::Query::Options), litecore::LiveQuerier*&, litecore::Query::Options&> (

    __t=<optimized out>, __f=<optimized out>) at /usr/include/c++/8/bits/invoke.h:89

#3  std::__invoke<void (litecore::LiveQuerier::*&)(litecore::Query::Options), litecore::LiveQuerier*&, litecore::Query::Options&> (__fn=<optimized out>)

    at /usr/include/c++/8/bits/invoke.h:95

#4  std::_Bind<void (litecore::LiveQuerier::*(litecore::LiveQuerier*, litecore::Query::Options))(litecore::Query::Options)>::__call<void, , 0ul, 1ul>(std::tuple<>&&, std::_Index_tuple<0ul, 1ul>) (__args=<optimized out>, this=<optimized out>) at /usr/include/c++/8/functional:400

#5  std::_Bind<void (litecore::LiveQuerier::*(litecore::LiveQuerier*, litecore::Query::Options))(litecore::Query::Options)>::operator()<, void>() (

    this=<optimized out>) at /usr/include/c++/8/functional:484

#6  std::_Function_handler<void (), std::_Bind<void (litecore::LiveQuerier::*(litecore::LiveQuerier*, litecore::Query::Options))(litecore::Query::Options)> >::_M_invoke(std::_Any_data const&) (__functor=...) at /usr/include/c++/8/bits/std_function.h:297

#7  0x00007f143c832642 in litecore::actor::ThreadedMailbox::safelyCall(std::function<void ()> const&) const (this=0x7f142801a3f8, f=...)

    at /home/couchbase/jenkins/workspace/couchbase-lite-c-debian9/couchbase-lite-c/vendor/couchbase-lite-core/LiteCore/Support/ThreadedMailbox.cc:217

#8  0x00007f143c832687 in litecore::actor::ThreadedMailbox::<lambda()>::operator() (__closure=0x7f1428047f60)

    at /home/couchbase/jenkins/workspace/couchbase-lite-c-debian9/couchbase-lite-c/vendor/couchbase-lite-core/LiteCore/Support/ThreadedMailbox.cc:159

#9  std::_Function_handler<void(), litecore::actor::ThreadedMailbox::enqueue(char const*, const std::function<void()>&)::<lambda()> >::_M_invoke(const std::_Any_data &) (__functor=...) at /usr/include/c++/8/bits/std_function.h:297

#10 0x00007f143c832801 in litecore::actor::ThreadedMailbox::performNextMessage (this=this@entry=0x7f142801a3f8)

    at /home/couchbase/jenkins/workspace/couchbase-lite-c-debian9/couchbase-lite-c/vendor/couchbase-lite-core/LiteCore/Support/ThreadedMailbox.cc:256

#11 0x00007f143c8328f6 in litecore::actor::Scheduler::task (this=0x7f14240881c0, taskID=1)

    at /home/couchbase/jenkins/workspace/couchbase-lite-c-debian9/couchbase-lite-c/vendor/couchbase-lite-core/LiteCore/Support/ThreadedMailbox.cc:107

#12 0x00007f143c96727f in execute_native_thread_routine () from /home/vagrant/ctestserver/libcblite.so.3

#13 0x00007f143c4d34a4 in start_thread (arg=0x7f1438888700) at pthread_create.c:456

#14 0x00007f1439840d0f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:97