Add null pointer checks for the src_a parameters
Add null pointer checks for the src_a parameters

Change-Id: Icc96e18eab07080c18b6542171a340c97f059c78
Reviewed-on: https://chromium-review.googlesource.com/c/libyuv/libyuv/+/3550016
Reviewed-by: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@chromium.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@chromium.org>

lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv,lemenkov/libyuv