Refactor local_useless_subtensor to allow earlier exiting of the function

theano/tensor/opt.py

@@ -1947,15 +1947,17 @@ def local_useless_subtensor(node):
                 # is not a useless subtensor
                 return False
 
-            length_pos_data = maxsize
+        for pos, idx in enumerate(cdata):
 
             length_pos = shape_of[node.inputs[0]][pos]
+
+            if isinstance(idx.stop, (int, numpy.integer)):
+                length_pos_data = maxsize
                 try:
                     length_pos_data = get_scalar_constant_value(length_pos)
                 except NotScalarConstantError:
                     pass
 
-            if isinstance(idx.stop, (int, numpy.integer)):
                 if idx.stop < length_pos_data:
                     return False
             elif isinstance(idx.stop, gof.Variable):