Deoldify Vapoursynth filter

[Dan64]

Ok, I understand that is not easy to use None in the GUI, also ref_tresh is None, but you pass always a value.

So you can pass ref_freq=0 if the user has not selected a different value.

If ref_freq = 0 (or None) will be applied the following default values:

   If ref_merge is enabled, ref_freq is set to 0
   If method=5 ref_freq is set to DEF_MIN_FREQ (=15)

It is necessary also to change the rule to set core.num_threads=1.
Currently num_threads=1 is set every time is checked "Reference frame only".
Now is necessary to set num_threads=1 when:  is checked "Reference frame only"  AND  (0 < SC SSIM thresh < 1 OR SC min int > 1)

Thanks,
Dan