Make sure a 64-bit char is never passed to ENCODE_CHAR.

Make sure a 64-bit char is never passed to ENCODE_CHAR.

This is for reasons similar to the recent CHAR_STRING fix.
* charset.c (Fencode_char): Check that character arg is actually
a character.  Pass an int to ENCODE_CHAR.
* charset.h (ENCODE_CHAR): Verify that the character argument is no
wider than 'int', as a compile-time check to prevent future regressions
in this area.