bug#13177: 24.3.50; doc of `read-char-by-name'

[Drew Adams]

> > The problem for me is that I don't know what the intention (design)
> > was or why.  Maybe someone has a good reason to return nil or to
> > return a number that does not correspond to a recognized code point?
> 
> It's called "read-char-by-name", so the intention is pretty clear: it
> should return a char.

Great.  That's what I would prefer also.  And that was exactly what I said in
the original bug report: that's what the other `read*' functions do: return the
thing their names say they read.

So we start with a code bug - make sure it always returns a char.  Then we fix
the doc.

However, this function has been around for a while, so there might be some code
that expects it to sometimes return nil or sometimes a non code-point number.
Hopefully, any code expecting nil is only trying to workaround this same bug...

Anyway, FWIW you've got my vote in favor of fixing the code to always return a
char.