bug#32627: 27.0.50; todo-show problems when adding and deleting new todo file

[Stephen Berman]

By default `M-x todo-show' from any buffer displays the todo category
(and hence the todo file) that was last displayed (or the default file
and category).  But after adding a new todo file (`F a' from todo-mode),
`M-x todo-show' always returns to it, even when another todo file has
been visited in between.  In the latter case, this is a bug, the other
todo file should be displayed.  Secondly, if you switch to the newly
added file from a non-todo-mode buffer and the delete the file (`F k'),
so that the current buffer is not in todo-mode, now `M-x todo-show' is a
noop the first time, but repeating it now correctly displays the
previous (or the default) todo file; this should happen with the first
invocation.

I have a fix for these problems and a test, which I'll commit to master.


In GNU Emacs 27.0.50 (build 22, x86_64-pc-linux-gnu, GTK+ Version 3.22.28)
 of 2018-09-03 built on rosalinde
Repository revision: 7e24039a9747cc1117b17631511e42cb3576362b