bug#11890: 24.1; (wrong-type-argument processp nil) in `shell-mode'

[Drew Adams <drew.adams@oracle.com>]

> > The command should not just barf with a wrong-type error msg.
> > As the bug report says:
> >
> >   Clearly, this code in shell.el is not tolerant of there being no
> >   process:
> >
> >   (file-name-nondirectory
> >    (car (process-command (get-buffer-process (current-buffer)))))
> >
> >   I imagine that it should be, or rather that it should perhaps raise an
> >   error with a more suitable message.
> 
> There are many functions that may fail if called with invalid parameters
> or in invalid buffers.  Emacs does not attempt to cover them all with
> user-level error messages.
> 
> If you don't have a recipe here, I don't see what how to proceed
> further, and I'm closing this bug report.

How to proceed is to make the `shell-mode' code ensure that if
there is no process then it raises an error saying that there
is no process.  The low-level error is the wrong error.