The original src_u calculation of FOURCC_I420 shifted half width if
crop_y is odd.
This CL fixs the problem and also add a test case for it.

Bug: b:115278653
Test: pass libyuv_unittest
Change-Id: Ia9732d22e64e13de26df47726ba44ad1c5a06484
Reviewed-on: https://chromium-review.googlesource.com/c/1258743Reviewed-by: Frank Barchard <fbarchard@chromium.org>