(fix): setting with pd.Series on Dataset (#2018)

* (fix): setting with `pd.Series` on `Dataset`

* (chore): relnote

* (fix): rename incoming index

* (fix): handle `None`

Author: ilan-gold

docs/release-notes/2018.bugfix.md

@@ -0,0 +1 @@
+Fix {func}`anndata.experimental.backed.Dataset2D.reindex` internal setting {user}`ilan-gold`

src/anndata/_core/xarray.py

@@ -389,9 +389,12 @@ def reindex(
         }
         el = self.ds.drop_vars(extension_arrays.keys())
         el = el.reindex({index_dim: index}, method=None, fill_value=fill_value)
-        for col in self.ds:
-            el[col] = pd.Series(self.ds[col], index=self.index).reindex(
-                index, fill_value=fill_value
+        for col, data in extension_arrays.items():
+            el[col] = XDataArray.from_series(
+                pd.Series(data.data, index=self.index).reindex(
+                    index.rename(self.index.name) if index is not None else index,
+                    fill_value=fill_value,
+                )
             )
         return Dataset2D(el)