Fix bug where Otsu thresholding ignored roi_method='ignore'

slideflow/slide/qc/otsu.py

@@ -123,7 +123,7 @@ def _thumb_from_slide(
             thumb = thumb[:, :, :3]
 
         # Only apply Otsu thresholding within ROI, if present
-        if len(wsi.roi_polys):
+        if wsi.has_rois():
             ofact = 1 / wsi.slide.level_downsamples[level]
             roi_mask = np.zeros((thumb.shape[0], thumb.shape[1]))
             scaled_polys = [