guake crashes when trying to close dead ssh session

- configuration
Guake Terminal: 3.5.0
VTE: 0.56.0
VTE runtime: 0.56.0
Gtk: 3.24.7
Gnome: 3.32.0 on wayland
Distro: Arch Linux
- problem
I open a ssh in guake. Because of slow network, ssh can't respond any input. I have to close the tab by right click it and select `close`, guake crashes immediately. Such situation has happend several times. Below is stack trace:
```
Stack trace of thread 28044:
#0 0x00007fd4a6ff0d7f raise (libc.so.6)
#1 0x00007fd4a6fdb672 abort (libc.so.6)
#2 0x00007fd4a6fdb548 __assert_fail_base.cold.0 (libc.so.6)
#3 0x00007fd4a6fe9396 __assert_fail (libc.so.6)
#4 0x00007fd4a4a9da71 n/a (libX11.so.6)
#5 0x00007fd4a4a9db21 n/a (libX11.so.6)
#6 0x00007fd4a4a9df85 _XReadEvents (libX11.so.6)
#7 0x00007fd4a4a85573 XIfEvent (libX11.so.6)
#8 0x00007fd4a38e860d gdk_x11_get_server_time (libgdk-3.so.0)
#9 0x00007fd4a2e44aeb n/a (libgtk-3.so.0)
#10 0x00007fd4a2e44e06 n/a (libgtk-3.so.0)
#11 0x00007fd4a2e45352 gtk_clipboard_set_with_data (libgtk-3.so.0)
#12 0x00007fd4a2e467c0 gtk_clipboard_set_text (libgtk-3.so.0)
#13 0x00007fd4a25a567c n/a (libvte-2.91.so.0)
#14 0x00007fd4a25c88cb n/a (libvte-2.91.so.0)
#15 0x00007fd4a25b1165 n/a (libvte-2.91.so.0)
#16 0x00007fd4a5232440 g_object_unref (libgobject-2.0.so.0)
#17 0x00007fd4a5407ab3 n/a (_gi.cpython-37m-x86_64-linux-gnu.so)
#18 0x00007fd4a6df73bd n/a (libpython3.7m.so.1.0)
#19 0x00007fd4a6dcbc78 n/a (libpython3.7m.so.1.0)
#20 0x00007fd4a6dac20b _PyDict_DelItem_KnownHash (libpython3.7m.so.1.0)
#21 0x00007fd4a6dac776 _PyObjectDict_SetItem (libpython3.7m.so.1.0)
#22 0x00007fd4a6dfade3 _PyObject_GenericSetAttrWithDict (libpython3.7m.so.1.0)
#23 0x00007fd4a6dfb296 PyObject_SetAttr (libpython3.7m.so.1.0)
#24 0x00007fd4a6e040a6 _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#25 0x00007fd4a6d956db _PyFunction_FastCallKeywords (libpython3.7m.so.1.0)
#26 0x00007fd4a6e02032 _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#27 0x00007fd4a6d956db _PyFunction_FastCallKeywords (libpython3.7m.so.1.0)
#28 0x00007fd4a6e02032 _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#29 0x00007fd4a6d4fdbb _PyFunction_FastCallDict (libpython3.7m.so.1.0)
#30 0x00007fd4a6d5f818 _PyObject_Call_Prepend (libpython3.7m.so.1.0)
#31 0x00007fd4a6d5049b PyObject_Call (libpython3.7m.so.1.0)
#32 0x00007fd4a6e7ee97 n/a (libpython3.7m.so.1.0)
#33 0x00007fd4a6e26fa5 n/a (libpython3.7m.so.1.0)
#34 0x00007fd4a7184a9d start_thread (libpthread.so.0)
#35 0x00007fd4a70b4b23 __clone (libc.so.6)

Stack trace of thread 1709:
#0 0x00007fd4a70a9c21 __poll (libc.so.6)
#1 0x00007fd4a52c8690 n/a (libglib-2.0.so.0)
#2 0x00007fd4a52c877e g_main_context_iteration (libglib-2.0.so.0)
#3 0x00007fd4a52c87d2 n/a (libglib-2.0.so.0)
#4 0x00007fd4a52a3c21 n/a (libglib-2.0.so.0)
#5 0x00007fd4a7184a9d start_thread (libpthread.so.0)
#6 0x00007fd4a70b4b23 __clone (libc.so.6)

Stack trace of thread 1710:
#0 0x00007fd4a70a9c21 __poll (libc.so.6)
#1 0x00007fd4a52c8690 n/a (libglib-2.0.so.0)
#2 0x00007fd4a52c877e g_main_context_iteration (libglib-2.0.so.0)
#3 0x00007fd4a2916bde n/a (libdconfsettings.so)
#4 0x00007fd4a52a3c21 n/a (libglib-2.0.so.0)
#5 0x00007fd4a7184a9d start_thread (libpthread.so.0)
#6 0x00007fd4a70b4b23 __clone (libc.so.6)

Stack trace of thread 1603:
#0 0x00007fd4a70a9c21 __poll (libc.so.6)
#1 0x00007fd4a52c8690 n/a (libglib-2.0.so.0)
#2 0x00007fd4a52c96d2 g_main_loop_run (libglib-2.0.so.0)
#3 0x00007fd4a2cd394f gtk_main (libgtk-3.so.0)
#4 0x00007fd4a5a126d0 ffi_call_unix64 (libffi.so.6)
#5 0x00007fd4a5a120a0 ffi_call (libffi.so.6)
#6 0x00007fd4a53f0684 n/a (_gi.cpython-37m-x86_64-linux-gnu.so)
#7 0x00007fd4a53efc6c n/a (_gi.cpython-37m-x86_64-linux-gnu.so)
#8 0x00007fd4a6d5049b PyObject_Call (libpython3.7m.so.1.0)
#9 0x00007fd4a6e0383e _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#10 0x00007fd4a6d4ed09 _PyEval_EvalCodeWithName (libpython3.7m.so.1.0)
#11 0x00007fd4a6d95882 _PyFunction_FastCallKeywords (libpython3.7m.so.1.0)
#12 0x00007fd4a6e066ea _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#13 0x00007fd4a6d956db _PyFunction_FastCallKeywords (libpython3.7m.so.1.0)
#14 0x00007fd4a6e0222d _PyEval_EvalFrameDefault (libpython3.7m.so.1.0)
#15 0x00007fd4a6d4ed09 _PyEval_EvalCodeWithName (libpython3.7m.so.1.0)
#16 0x00007fd4a6d4fc64 PyEval_EvalCodeEx (libpython3.7m.so.1.0)
#17 0x00007fd4a6d4fc8c PyEval_EvalCode (libpython3.7m.so.1.0)
#18 0x00007fd4a6e78694 n/a (libpython3.7m.so.1.0)
#19 0x00007fd4a6e79b6e PyRun_FileExFlags (libpython3.7m.so.1.0)
#20 0x00007fd4a6e7d035 PyRun_SimpleFileExFlags (libpython3.7m.so.1.0)
#21 0x00007fd4a6e7f2a7 n/a (libpython3.7m.so.1.0)
#22 0x00007fd4a6e7f4ec _Py_UnixMain (libpython3.7m.so.1.0)
#23 0x00007fd4a6fdd223 __libc_start_main (libc.so.6)
#24 0x000055820452d05e _start (python3.7)

Stack trace of thread 1711:
#0 0x00007fd4a70a9c21 __poll (libc.so.6)
#1 0x00007fd4a52c8690 n/a (libglib-2.0.so.0)
#2 0x00007fd4a52c96d2 g_main_loop_run (libglib-2.0.so.0)
#3 0x00007fd4a5029568 n/a (libgio-2.0.so.0)
#4 0x00007fd4a52a3c21 n/a (libglib-2.0.so.0)
#5 0x00007fd4a7184a9d start_thread (libpthread.so.0)
#6 0x00007fd4a70b4b23 __clone (libc.so.6)
```