avfilter/vf_lut: make it possible to clip pixel values that are out of valid range

Previous behavior was not useful at all as such pixels where all mapped to 0.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_lut.c

@@ -310,7 +310,7 @@ static int config_props(AVFilterLink *inlink)
         s->var_values[VAR_MAXVAL] = max[color];
         s->var_values[VAR_MINVAL] = min[color];
 
-        for (val = 0; val < (1 << desc->comp[0].depth); val++) {
+        for (val = 0; val < FF_ARRAY_ELEMS(s->lut[comp]); val++) {
             s->var_values[VAR_VAL] = val;
             s->var_values[VAR_CLIPVAL] = av_clip(val, min[color], max[color]);
             s->var_values[VAR_NEGVAL] =