Fix expansion and encoding of sound file names on MS-Windows.

Fix expansion and encoding of sound file names on MS-Windows.

 src/sound.c (Fplay_sound_internal): Encode the sound file name in
 the ANSI codepage.  Expand it against data-directory, as per docs,
 not against the current directory.  No need to make a local copy
 of the file name; pass the encoded file name directly to
 do_play_sound.  (Bug#18463)
 src/w32.c (ansi_encode_filename): If w32_get_short_filename returns
 NULL, and the file name is not encodable in ANSI codepage, return
 the string with "?" replacement characters, which will fail the
 caller.  This avoids returning a random value in that case.