bug#70988: (read FUNCTION) uses Latin-1 [PATCH]

[Mattias Engdegård]

When `read` is called with a function as stream argument, the return values of 
that function are often interpreted as Latin-1 characters with only the 8 low 
bits used. Example:

(let* ((next '(?A #x12a nil))
       (f (lambda (&rest args)
            (if args
                (push (car args) next)
              (pop next)))))
  (read f))
=> A*   ; expected: AĪ

This is a result of `readchar` setting *multibyte to 0 on this code path.

The reader is not very consistent: inside string and character literals, the 
code seems to work as expected.

The fix is straightforward (attached).

read-from-function.diff
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