simplify code a bit

Author: charlesdong1991

pandas/io/formats/csvs.py

@@ -213,21 +213,20 @@ def _index_label_encoder(self):
         obj = self.obj
 
         if index_label is True:
+            index_label = []
             # append index label based on index type
             if isinstance(obj.index, ABCMultiIndex):
-                index_label = []
                 for name in obj.index.names:
                     # add empty string is name is None
                     if name is None:
                         name = ''
                     index_label.append(name)
             else:
-                index_label = obj.index.name
                 # if no name, use empty string
-                if index_label is None:
-                    index_label = ['']
+                if obj.index.name is None:
+                    index_label.append('')
                 else:
-                    index_label = [index_label]
+                    index_label.append(obj.index.name)
         elif not isinstance(index_label,
                             (list, tuple, np.ndarray, ABCIndexClass)):
             index_label = [index_label]