more cleanup

xarray/core/dataset.py

@@ -2993,19 +2993,20 @@ def isel(
             # underlying array's shape and ndim since the dims are already
             # cached by the Variable
             var_dims = var.dims
-            # preserve variable order
-            if name in index_variables:
-                var = index_variables[name]
             # Fastpath, skip all this metadata analysis for variables
             # with no dimensions
-            elif var_dims and (var_indexer_keys := all_keys.intersection(var_dims)):
-                var_indexers = {k: indexers[k] for k in var_indexer_keys}
-                var = var.isel(var_indexers)
-                if drop and var.ndim == 0 and name in coord_names:
-                    coord_names.remove(name)
-                    continue
+            if var_dims:
+                # preserve variable order
+                if name in index_variables:
+                    var = index_variables[name]
+                elif var_indexer_keys := all_keys.intersection(var_dims):
+                    var_indexers = {k: indexers[k] for k in var_indexer_keys}
+                    var = var.isel(var_indexers)
+                    if drop and var.ndim == 0 and name in coord_names:
+                        coord_names.remove(name)
+                        continue
             variables[name] = var
-            dims.update(zip(var.dims, var.shape))
+            dims.update(zip(var_dims, var.shape))
 
         return self._construct_direct(
             variables=variables,