opt: reject denominator zero as out of range

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>

libavutil/opt.c

@@ -97,7 +97,7 @@ static int read_number(const AVOption *o, const void *dst, double *num, int *den
 static int write_number(void *obj, const AVOption *o, void *dst, double num, int den, int64_t intnum)
 {
     if (o->type != AV_OPT_TYPE_FLAGS &&
-        (o->max * den < num * intnum || o->min * den > num * intnum)) {
+        (!den || o->max * den < num * intnum || o->min * den > num * intnum)) {
         num = den ? num * intnum / den : (num * intnum ? INFINITY : NAN);
         av_log(obj, AV_LOG_ERROR, "Value %f for parameter '%s' out of range [%g - %g]\n",
                num, o->name, o->min, o->max);