DO NOT MERGE | libvpx: cherry pick fix to OOB of mv_cost index. Bug: b/72510002 Test: poc provided in the bug. Change-Id: I011763cd35b3bac1621e19e4447c442a39d66011 (cherry picked from commit 073990fb32f39c64e4ba9cbd5fb11bfc0c1f0aad)