avoid unnecessary indentation level

Cython/Compiler/PyrexTypes.py

@@ -47,7 +47,9 @@ class BaseType(object):
 
     def get_fused_types(self, result=None, seen=None, subtypes=None):
         subtypes = subtypes or self.subtypes
-        if subtypes:
+        if not subtypes:
+            return None
+
         if result is None:
             result = []
             seen = set()
@@ -63,8 +65,6 @@ class BaseType(object):
 
         return result
 
-        return None
-
     def specialize_fused(self, env):
         if env.fused_to_specific:
             return self.specialize(env.fused_to_specific)