bug#69454: Not possible to insert an empty vtable

[Eli Zaretskii]

> Date: Wed, 28 Feb 2024 15:29:11 +0100
> From: Eric Marsden <eric.marsden@risk-engineering.org>
> 
> Hello,
> 
> The following generates an error. It seems to me that it would be 
> preferable to insert the header line and show zero rows for the vtable.
> 
>     (require 'vtable)
>     (make-vtable :columns '("tweedle" "dum") :objects (list))
> 
> Debugger entered--Lisp error: (wrong-number-of-arguments #<subr max> 0)
>    max()
>    apply(max nil)
>    seq-max(nil)

I'm not sure we want to support zero-size vtables.  A better error
message would be nice, though.  What do others think?

P.S. Adam, I took the liberty of adding you to this discussion, since
you seem lately to be interested in vtable.