unencodable-char-position bug?

[Paul Pogonyshev]

Hi,

Is it correct that

        (unencodable-char-position 0 1 'utf-8 nil "ы")

evaluates to 0?  Since UTF-8 can encode anything, I presume the
correct return value would be nil...  The result is the same if
tried on a Russian letter character in a buffer instead of a
string.

In general, what is the best way to determine if given character
is encodable in given coding system?

Paul