Ticket #256 (segfault in backward_word)

fixed segfault in backward_word (widget.c)
    ...
    The for loop, whose purpose is to remove exactly 1 character
    (hence I don't get why it's a loop, but nevermind) was not UTF8-ready.
    So if the character preceding the cursor was an accented one,
    it jumped to the middle of the UTF-8 sequence, causing the rest of
    the stuff go unpredictable.

    Although it *should* never happen (which, as we all know,
    does not equal to "never happens"), in this case "p" simply jumped
    over "in->buffer". The function has a "p != in->buffer" check three times,
    it might it more robust if you replaced that with "p >= in->buffer".
    This should prevent the segfault, and just stay with a slightly buggy but
    otherwise harmless alt-backspace behavior, should there be any UTF-8 or
    similar bugs left. This change is not included in my patch.

Signed-off-by: Ilia Maslakov <il.smind@gmail.com>

src/widget.c

@@ -1490,7 +1490,7 @@ backward_word (WInput *in)
     for (
         p = in->buffer + str_offset_to_pos (in->buffer, in->point);
         (p != in->buffer) && (p[0] == '\0');
-        p-- , in->point--
+        str_cprev_char (&p), in->point--
     );
 
     while (p != in->buffer) {