bug#45474: Icomplete exhibiting in recursive minibuffer when it shouldn’t

[Stefan Monnier]

> I tested your patch and discovered that it fails when two nested
> minibuffers both use completion, e.g. C-x C-f C-h v raises the error:
>
>    Error in post-command-hook (icomplete-post-command-hook): 
> (wrong-type-argument symbolp

Indeed, it's nasty:

- In the first step, we
  - let-bind (globally) m-c-table to read-file-name-internal
  - go to minibuf-1
  - make it buffer-local in minibuf-1
  - everything's dandy
- In the second step, things get ugly
  - we're in minibuf-1
  - we let-bind m-c-table to help--symbol-completion-table which
    only works buffer-locally in minibuf-1 (thus temporarily overriding
    the value set just before).
  - we go to minibuf-2 which still has no buffer-local setting so it
    sees the global value that's still read-file-name-internal (because
    of the very first part of the first step)
  - we make it buffer-local but to this wrong value

So in the end we get a wrong m-c-table in both buffers (the values are 
reversed!).


        Stefan