SEGV in EndRemoteBootstrapSession on bolt80

JD hit this issue on bolt80 when a server fell behind a bit:

• • • SIGSEGV (@0xc0) received by PID 2740 (TID 0x7ff40c160700) from PID 192; stack trace: ***
      @ 0x398660f500 (unknown)
      @ 0x717cfc (unknown)
      @ 0x714d9b (unknown)
      @ 0x71599c (unknown)
      @ 0x77b9dc (unknown)
      @ 0x931748 (unknown)
      @ 0x127265f (unknown)
      @ 0x3986607851 (unknown)
      @ 0x39862e894d (unknown)
      @ 0x0 (unknown)
      (gdb) info symbol 0x717cfc
      kudu::tserver::RemoteBootstrapSession::tablet_id() const + 108 in section .text
      (gdb) info symbol 0x714d9b
      kudu::tserver::RemoteBootstrapServiceImpl::DoEndRemoteBootstrapSessionUnlocked(std::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, kudu::tserver::RemoteBootstrapErrorPB_Code*) + 91 in section .text
      (gdb) info symbol 0x71599c
      kudu::tserver::RemoteBootstrapServiceImpl::EndRemoteBootstrapSession(kudu::tserver::EndRemoteBootstrapSessionRequestPB const*, kudu::tserver::EndRemoteBootstrapSessionResponsePB*, kudu::rpc::RpcContext*) + 252 in section .text