jpeg2000: Correctly calculate sgnd

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/jpeg2000dec.c

@@ -198,7 +198,7 @@ static int get_siz(Jpeg2000DecoderContext *s)
         uint8_t x    = bytestream2_get_byteu(&s->g);
         s->cbps[i]   = (x & 0x7f) + 1;
         s->precision = FFMAX(s->cbps[i], s->precision);
-        s->sgnd[i]   = (x & 0x80) == 1;
+        s->sgnd[i]   = !!(x & 0x80);
         s->cdx[i]    = bytestream2_get_byteu(&s->g);
         s->cdy[i]    = bytestream2_get_byteu(&s->g);