Fix handling of img_num=0 cases

skimage/io/_plugins/pil_plugin.py

@@ -114,6 +114,9 @@ def pil_to_ndarray(im, dtype=None, img_num=None):
         frames.append(frame)
         i += 1
 
+        if img_num is not None:
+            break
+
     if hasattr(im, 'fp') and im.fp:
         im.fp.close()
 

skimage/io/collection.py

@@ -254,7 +254,7 @@ class ImageCollection(object):
                 kwargs = self.load_func_kwargs
                 if self._frame_index:
                     fname, img_num = self._frame_index[n]
-                    if img_num > 0:
+                    if img_num is not None:
                         self.data[idx] = self.load_func(fname, img_num=img_num,
                                                         **kwargs)
                     else: