avfilter/vf_scale: simplify alignment code

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavfilter/vf_scale.c

@@ -273,22 +273,17 @@ static int config_props(AVFilterLink *outlink)
     h = scale->h;
 
     /* Check if it is requested that the result has to be divisible by a some
-     * factor (w or h = -n with n being the factor). After we got the factor,
+     * factor (w or h = -n with n being the factor). */
-     * we set w/h back to -1 so that the automatic scaling is done. */
     factor_w = 1;
     factor_h = 1;
     if (w < -1) {
         factor_w = -w;
-        w = -1;
-        scale->w = -1;
     }
     if (h < -1) {
         factor_h = -h;
-        h = -1;
-        scale->h = -1;
     }
 
-    if (w == -1 && h == -1)
+    if (w < 0 && h < 0)
         scale->w = scale->h = 0;
 
     if (!(w = scale->w))
@@ -299,9 +294,9 @@ static int config_props(AVFilterLink *outlink)
     /* Make sure that the result is divisible by the factor we determined
      * earlier. If no factor was set, it is nothing will happen as the default
      * factor is 1 */
-    if (w == -1)
+    if (w < 0)
         w = av_rescale(h, inlink->w, inlink->h * factor_w) * factor_w;
-    if (h == -1)
+    if (h < 0)
         h = av_rescale(w, inlink->h, inlink->w * factor_h) * factor_h;
 
     /* Note that force_original_aspect_ratio may overwrite the previous set