If a TUI window is written in Python, and if the window construction
function fails, then gdb will crash. This patch fixes the crash.
gdb/ChangeLog
2020-06-16 Tom Tromey <tom@tromey.com>
* python/py-tui.c (tui_py_window::~tui_py_window): Handle case
where m_window==nullptr.
gdb/testsuite/ChangeLog
2020-06-16 Tom Tromey <tom@tromey.com>
* gdb.python/tui-window.py (failwin): New function. Register it
as a TUI window type.
* gdb.python/tui-window.exp: Create new "fail" layout. Test it.