Improve maximum subarray for negative array

[fish-404]

Considerate if a array is all of negative numbers, it shouldn't return 0 as maximun subarray sum

[64json]

I think it is a correct behavior to return 0 for a negative array, since an empty array is also a subarray. Feel free to reopen it if you think otherwise.

[fish-404]

Hi, I think it depends on wheter we admit a empty is a subarray.
I meet this problem in LeetCode (No. 53). And the test case shown they won't regard empty array as a subarray. If the test case is a negative array, it will return the max negative num.
I check reference in Wikipia and GeeksforGeeks, GeeksforGeeks doesn't admit a empty as a subarray. And Wikipia expian the algorithms history, disallow empty subarrays is a variant of the problem.