Don't check most significant digit if we break out of the loop

[borundev]

In int_as_array_increment if we break out of the for loop, we do do not want to check the most significant digit. It is a minor O(1) improvement.

[tsunghsienlee]

Hi @borundev ,

Very smart use of the Python specific language feature to make this improvement. Really appreciate for your contribution, and this will be released in the next version.