Follow up PR: pandas-dev#28097 Simplify branch statement

Author: proost

pandas/core/indexes/multi.py

@@ -1304,14 +1304,13 @@ def _get_grouper_for_level(self, mapper, level):
             codes[mask] = ok_codes
             codes[~mask] = -1
 
-        if len(uniques) < len(level_index):
-            # Remove unobserved levels from level_index
-            level_index = level_index.take(uniques)
+            grouper = level_index.take(codes, fill_value=True)
+        else:
+            if len(uniques) < len(level_index):
+                # Remove unobserved levels from level_index
+                level_index = level_index.take(uniques)
 
-        if len(level_index):
             grouper = level_index.take(codes)
-        else:
-            grouper = level_index.take(codes, fill_value=True)
 
         return grouper, codes, level_index