libobs: Add ability to use scale filters on scene items

Allows the ability to use scale filters such as point, bicubic, lanczos
on specific scene items, disabled by default.  When using one of the
latter two options, if the item's scale is under half of the source's
original size, it uses the bilinear low resolution downscale shader
instead.

libobs/obs-video.c

@@ -126,7 +126,8 @@ static inline gs_effect_t *get_scale_effect_internal(
 	switch (video->scale_type) {
 	case OBS_SCALE_BILINEAR: return video->default_effect;
 	case OBS_SCALE_LANCZOS:  return video->lanczos_effect;
-	case OBS_SCALE_BICUBIC:;
+	case OBS_SCALE_BICUBIC:
+	default:;
 	}
 
 	return video->bicubic_effect;