Panic on busy mouse events

Problem: With the MouseTerminal in lxterminal, press mouse and drag the pointer outside of the terminal window and fiddle with it a lot => panic:

thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', libcore/option.rs:345:21
stack backtrace:
   0: std::sys::unix::backtrace::tracing::imp::unwind_backtrace
             at libstd/sys/unix/backtrace/tracing/gcc_s.rs:49
   1: std::sys_common::backtrace::print
             at libstd/sys_common/backtrace.rs:71
             at libstd/sys_common/backtrace.rs:59
   2: std::panicking::default_hook::{{closure}}
             at libstd/panicking.rs:211
   3: std::panicking::default_hook
             at libstd/panicking.rs:227
   4: std::panicking::rust_panic_with_hook
             at libstd/panicking.rs:511
   5: std::panicking::continue_panic_fmt
             at libstd/panicking.rs:426
   6: rust_begin_unwind
             at libstd/panicking.rs:337
   7: core::panicking::panic_fmt
             at libcore/panicking.rs:92
   8: core::panicking::panic
             at libcore/panicking.rs:53
   9: <core::option::Option<T>>::unwrap
             at /checkout/src/libcore/macros.rs:20
  10: termion::event::parse_csi::{{closure}}
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/event.rs:161
  11: termion::event::parse_csi
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/event.rs:166
  12: termion::event::parse_event
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/event.rs:118
  13: termion::input::parse_event
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/input.rs:99
  14: <termion::input::EventsAndRaw<R> as core::iter::iterator::Iterator>::next
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/input.rs:77
  15: <termion::input::Events<R> as core::iter::iterator::Iterator>::next
             at ~/.cargo/registry/src/github.com-1ecc6299db9ec823/termion-1.5.1/src/input.rs:38
  16: two::ui::grinui::GrinUI::process
             at src/ui/grinui.rs:59
  17: two::ui::grinui::GrinUI::react_once
             at src/ui/grinui.rs:54
  18: two::ui::grin::Grin::wait
             at src/ui/grin.rs:63
  19: two::main::{{closure}}
             at src/main.rs:23
  20: <core::result::Result<T, E>>::and_then
             at /checkout/src/libcore/result.rs:621
  21: two::main
             at src/main.rs:22
  22: std::rt::lang_start::{{closure}}
             at /checkout/src/libstd/rt.rs:74
  23: std::panicking::try::do_call
             at libstd/rt.rs:59
             at libstd/panicking.rs:310
  24: __rust_maybe_catch_panic
             at libpanic_unwind/lib.rs:105
  25: std::rt::lang_start_internal
             at libstd/panicking.rs:289
             at libstd/panic.rs:392
             at libstd/rt.rs:58
  26: std::rt::lang_start
             at /checkout/src/libstd/rt.rs:74
  27: main
  28: __libc_start_main
  29: _start