Fix out of bounds read in RP::load_tables_u16_be()

BUG=skia:

CQ_INCLUDE_TRYBOTS=skia.primary:Test-Ubuntu-GCC-GCE-CPU-AVX2-x86_64-Release-SKNX_NO_SIMD

Change-Id: I4f6dd002b03812d63bf62342c346ea21f6865466
Reviewed-on: https://skia-review.googlesource.com/7027
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Matt Sarett <msarett@google.com>
2 files changed