Debug 0 size reduction function

[ghost]

In #85 , we found reduction functions have bug.
Reduction functions meet problem if input was 0 size ndarray.
In vega, reduction function will be hangup ( if input was 0 size ndarray).
In titanv, reduction function raise error ( if input was 0 size ndarray).
In furyx has no problem.

In #207 , I implemented exception code to solve this issue.
And pass the test_truth test.

But, I think there will be better way to over come this issue without exception code.

[LWisteria]

@t-kitawaki Thank you for reporting. Can you provide steps to reproduce the bug?

[ghost]

To reproduce this issue, remove this code and run reduction function (like any all sum prod max min...) with 0 size input.

clpy/clpy/core/reduction.pxi

Lines 252 to 262 in 1de64f1

	# TODO(tomoharu.kitawaki): debug 0 size reduction and remove this
	if a.size == 0:
	if self.identity in ['true', 'false']:
	ret_identity = True if self.identity=='true' else False
	else:
	ret_identity = self.identity
	ret = clpy.empty(out_shape, out_types[0])
	ret.fill(ret_identity)
	if out is not None:
	out.fill(ret_identity)
	return ret

Easy way to run 0 size reduction function is run clpy_tests/logic_tests/test_truth.py lile #85 .