Fix size passed to fast filter evaluator (#672)

The evaluator uses the `estimated_output_size` internally but we were
passing only the idat size in the fast filter evaluator. At level `o2`,
or higher levels when using `--fast`, this could cause a slight bias
towards the None and Bigrams filters for indexed images. The actual
impact to results is incredibly minor but it's definitely incorrect so
we should fix it.

src/lib.rs

@@ -509,7 +509,7 @@ fn perform_trials(
                 opts.optimize_alpha,
             );
             if let Some(result) = &eval_result {
-                eval.set_best_size(result.idat_data.len());
+                eval.set_best_size(result.estimated_output_size());
             }
             eval.try_image(image.clone());
             if let Some(result) = eval.get_best_candidate() {