libjpegrecoverymap: solve recovery map 8-pixel alignment

JPEG encoder requires width to be 8 aligned, and the recovery map is downsampled by 4, so that the JPEG/R encoder will require width to be 32 aligned, which is not ideal. We should handle widths that are 8 aligned but not 32 aligned.

Test: recoverymap_test
Bug: b/264715926
Change-Id: I74eaeec7c16f8f2621e72c067464897c8aba9d89