Consolidate type checks in _decode_chunk

As refactoring of the `reshape` step has effectively dropped the
expected `object` type case, the checks for different types is a little
more complicated than needed. To fix this, basically invert and swap the
case ordering. This way we can handle all generally expected types first
and simply cast them. Then we can raise if an `object` type shows up and
is unexpected.

Author: jakirkham

zarr/core.py

@@ -1746,18 +1746,17 @@ def _decode_chunk(self, cdata):
 
         # view as numpy array with correct dtype
         chunk = ensure_ndarray(chunk)
-        if self._dtype == object:
-            # special case object dtype, because incorrect handling can lead to
-            # segfaults and other bad things happening
-            if chunk.dtype != object:
-                # If we end up here, someone must have hacked around with the filters.
-                # We cannot deal with object arrays unless there is an object
-                # codec in the filter chain, i.e., a filter that converts from object
-                # array to something else during encoding, and converts back to object
-                # array during decoding.
-                raise RuntimeError('cannot read object array without object codec')
-        else:
+        # special case object dtype, because incorrect handling can lead to
+        # segfaults and other bad things happening
+        if self._dtype != object:
             chunk = chunk.view(self._dtype)
+        elif chunk.dtype != object:
+            # If we end up here, someone must have hacked around with the filters.
+            # We cannot deal with object arrays unless there is an object
+            # codec in the filter chain, i.e., a filter that converts from object
+            # array to something else during encoding, and converts back to object
+            # array during decoding.
+            raise RuntimeError('cannot read object array without object codec')
 
         # ensure correct chunk shape
         chunk = chunk.reshape(-1, order='A')