turbojpeg.h: Parenthesize TJSCALED() dimension arg

This ensures that, for example,
TJSCALED(dim0 + dim1, sf)

will evaluate to
(((dim0 + dim1) * sf.num + sf.denom - 1) / sf.denom)

rather than
((dim0 + (dim1 * sf.num) + sf.denom - 1) / sf.denom)

turbojpeg.h

diff --git a/turbojpeg.h b/turbojpeg.h
index 7610221..7a3d07b 100644
--- a/turbojpeg.h
+++ b/turbojpeg.h
@@ -487,7 +487,7 @@
  * factor.  This macro performs the integer equivalent of <tt>ceil(dimension *
  * scalingFactor)</tt>. 
  */
-#define TJSCALED(dimension, scalingFactor) ((dimension * scalingFactor.num \
+#define TJSCALED(dimension, scalingFactor) (((dimension) * scalingFactor.num \
   + scalingFactor.denom - 1) / scalingFactor.denom)