Camera: Fix buffer underflow in ImageReaderTest

In convertPixelYuvToRgba(), NV21 format could cause buffer underflow
since for each row and channel (pixel stride * width) bytes are read,
and Cb pixels start at offset 1. Fix it by reading
(pixel stride * (width - 1) + 1) bytes.

Bug: 199337639
Test: atest -d android.hardware.camera2.cts.ImageReaderTest#testAllOutputYUVResolutions
Change-Id: I6084cef70b5b1d28bfb67695e83efa23be0c64a3