bug#63648: 29.0.90; project.el: with switch-use-entire-map, switch-project errors on non-project commands

[Juri Linkov]

>> https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63829 was a problem
>> caused by a similar approach in the implementation. OTOH,
>
> I was thinking we'd solve both this specific problem and the general
> case by just saving the current buffer in a project-old-buffer variable
> so that project-aware commands could go back and grab stuff from it.
>
> It does mean that project-unaware commands can't both operate in a
> different project and on the current buffer.  Is there ever a place we
> actually want that though?

For example, 'C-x p p M-x rgrep RET' would need to read a word under point
as the default value.