pil_cv2.check_dpi: fix class membership test

(depending on how the `PIL.Image` was instantiated – file plugin or array interface – the previous `isinstance` could fail, provoking a fall-through to `cv2pil` which does not work)

qurator/eynollah/utils/pil_cv2.py

@@ -16,7 +16,7 @@ def pil2cv(img):
 
 def check_dpi(img):
     try:
-        if isinstance(img, Image.__class__):
+        if isinstance(img, Image.Image):
             pil_image = img
         elif isinstance(img, str):
             pil_image = Image.open(img)