Interlaced encoding causes crash

[JDarnley]

Trying to use interlaced encoding causes a segfault in the transform. The crash happens in all wavelets available, an example backtrace for haar is below.

Arch Linux, x86-64, kernel 4.9.78-1, Boost 1.66.0-1, gcc 7.2.1+20180116-1.

gdb backtrace:

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Reading symbols from ./testprogs/vc2encode...done.
(gdb) r
Starting program: /home/james/src/vc2hqencode/testprogs/vc2encode --interlace --threads=1 --wavelet=haar1
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib/libthread_db.so.1".
INFO: Processor Features:
INFO:   SSE4.2 [ ]
INFO:   AVX    [ ]
INFO:   AVX2   [ ]
INFO: VC2Encoder.cpp:281: Configuring for 1 threads, 4 jobs

[New Thread 0x7ffff66da700 (LWP 24326)]

Thread 2 "vc2encode" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7ffff66da700 (LWP 24326)]
Haar_transform_H_inplace_10P2<1, short> (_idata=0x0, istride=3840, _odata=_odata@entry=0x7ffff66d9cd0, ostride=1920, iwidth=1920, iheight=136, owidth=1920, oheight=136)
    at haar_transform.hpp:153
153           int32_t D   = (((int32_t)idata[y*istride + x]) - offset) << shift;
(gdb) bt
#0  Haar_transform_H_inplace_10P2<1, short> (_idata=0x0, istride=3840, _odata=_odata@entry=0x7ffff66d9cd0, ostride=1920, iwidth=1920, iheight=136, owidth=1920, oheight=136)
    at haar_transform.hpp:153
#1  0x000055555557da54 in VC2Encoder::Transform<short> (this=0x555555825570, _job=<optimized out>) at VC2Encoder.cpp:1016
#2  0x000055555557df54 in boost::_mfi::mf1<void, VC2Encoder, JobBase*>::operator() (a1=0x55555582d4c0, p=0x555555825570, this=<optimized out>)
    at /usr/include/boost/bind/mem_fn_template.hpp:165
#3  boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> >::operator()<boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list0> (a=<synthetic pointer>...,
    f=<synthetic pointer>..., this=<synthetic pointer>) at /usr/include/boost/bind/bind.hpp:319
#4  boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > >::operator() (
    this=<synthetic pointer>) at /usr/include/boost/bind/bind.hpp:1294
#5  boost::asio::asio_handler_invoke<boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > > > (function=<synthetic pointer>...) at /usr/include/boost/asio/handler_invoke_hook.hpp:69
#6  boost_asio_handler_invoke_helpers::invoke<boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > >, boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > > > (
    context=<synthetic pointer>..., function=<synthetic pointer>...) at /usr/include/boost/asio/detail/handler_invoke_helpers.hpp:37
#7  boost::asio::detail::handler_work<boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > >, boost::asio::system_executor>::complete<boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > > > (this=<synthetic pointer>, handler=<synthetic pointer>..., function=<synthetic pointer>...) at /usr/include/boost/asio/detail/handler_work.hpp:82
#8  boost::asio::detail::completion_handler<boost::_bi::bind_t<void, boost::_mfi::mf1<void, VC2Encoder, JobBase*>, boost::_bi::list2<boost::_bi::value<VC2Encoder*>, boost::_bi::value<JobBase*> > > >::do_complete (owner=0x55555582d090, base=<optimized out>) at /usr/include/boost/asio/detail/completion_handler.hpp:70
#9  0x0000555555582dd9 in boost::asio::detail::scheduler_operation::complete (bytes_transferred=0, ec=..., owner=0x55555582d090, this=<optimized out>)
    at /usr/include/boost/asio/detail/scheduler_operation.hpp:40
#10 boost::asio::detail::scheduler::do_run_one (ec=..., this_thread=..., lock=..., this=0x55555582d090) at /usr/include/boost/asio/detail/impl/scheduler.ipp:401
#11 boost::asio::detail::scheduler::run (ec=..., this=0x55555582d090) at /usr/include/boost/asio/detail/impl/scheduler.ipp:154
#12 boost::asio::io_context::run (this=0x55555582cde8) at /usr/include/boost/asio/impl/io_context.ipp:62
#13 ThreadPool::_run (this=0x55555582cde0) at ThreadPool.hpp:132
#14 0x00007ffff79bf7bf in ?? () from /usr/lib/libboost_thread.so.1.66.0
#15 0x00007ffff738308c in start_thread () from /usr/lib/libpthread.so.0
#16 0x00007ffff67d0e7f in clone () from /usr/lib/libc.so.6