net: avoid UB in WebSocketHandler::readPayload()
Seen when closing a Writer document.
/home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/stl_vector.h:798:9: runtime error: reference binding to null pointer of type 'char'
#0 0x6ff633 in std::vector<char, std::allocator<char> >::operator[](unsigned long) /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/stl_vector.h:798:2
#1 0x770d0c in WebSocketHandler::readPayload(unsigned char*, unsigned long, unsigned char*, std::vector<char, std::allocator<char> >&) /home/vmiklos/lode/dev/online/./net/WebSocketHandler.hpp:611:29
#2 0x759324 in WebSocketHandler::handleTCPStream(std::shared_ptr<StreamSocket> const&) /home/vmiklos/lode/dev/online/./net/WebSocketHandler.hpp:251:13
#3 0x6f820d in WebSocketHandler::handleIncomingMessage(SocketDisposition&) /home/vmiklos/lode/dev/online/./net/WebSocketHandler.hpp:419:20
#4 0xb2da64 in ClientSession::handleIncomingMessage(SocketDisposition&) /home/vmiklos/lode/dev/online/wsd/ClientSession.cpp:74:14
#5 0xa70a61 in StreamSocket::handlePoll(SocketDisposition&, std::chrono::time_point<std::chrono::_V2::steady_clock, std::chrono::duration<long, std::ratio<1l, 1000000000l> > >, int) /home/vmiklos/lode/dev/online/./net/Socket.hpp:1037:29
#6 0x6ec83d in SocketPoll::poll(int) /home/vmiklos/lode/dev/online/./net/Socket.hpp:570:34
#7 0x830019 in DocumentBroker::pollThread() /home/vmiklos/lode/dev/online/wsd/DocumentBroker.cpp:286:16
#8 0x8fdb38 in DocumentBroker::DocumentBrokerPoll::pollingThread() /home/vmiklos/lode/dev/online/wsd/DocumentBroker.cpp:165:20
#9 0xe00e75 in SocketPoll::pollingThreadEntry() /home/vmiklos/lode/dev/online/net/Socket.cpp:184:9
#10 0xe49cfd in void std::__invoke_impl<void, void (SocketPoll::*)(), SocketPoll*>(std::__invoke_memfun_deref, void (SocketPoll::*&&)(), SocketPoll*&&) /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/invoke.h:73:14
#11 0xe4980a in std::__invoke_result<void (SocketPoll::*)(), SocketPoll*>::type std::__invoke<void (SocketPoll::*)(), SocketPoll*>(void (SocketPoll::*&&)(), SocketPoll*&&) /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/invoke.h:95:14
#12 0xe496bd in decltype(std::__invoke(_S_declval<0ul>(), _S_declval<1ul>())) std:🧵:_Invoker<std::tuple<void (SocketPoll::*)(), SocketPoll*> >::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/thread:234:13
#13 0xe494c7 in std:🧵:_Invoker<std::tuple<void (SocketPoll::*)(), SocketPoll*> >::operator()() /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/thread:243:11
#14 0xe4888a in std:🧵:_State_impl<std:🧵:_Invoker<std::tuple<void (SocketPoll::*)(), SocketPoll*> > >::_M_run() /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/thread:186:13
#15 0x7f2c5805fe2e in execute_native_thread_routine /home/vmiklos/lode/packages/gccbuild/x86_64-pc-linux-gnu/libstdc++-v3/src/c++11/../../../../../gcc-7.3.0/libstdc++-v3/src/c++11/thread.cc:83
#16 0x7f2c57a3c558 in start_thread (/lib64/libpthread.so.0+0x7558)
#17 0x7f2c5715082e in clone (/lib64/libc.so.6+0xf882e)
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior /home/vmiklos/lode/opt_private/gcc-7.3.0/lib/gcc/x86_64-pc-linux-gnu/7.3.0/../../../../include/c++/7.3.0/bits/stl_vector.h:798:9 in
Change-Id: Ifaf6b193e9bba480587c2e184df55aa0728bb370
4e1ed7205d