cast to unsigned before shifting

Otherwise we can appear to convert signed to unsigned.

Change-Id: I66ce3891dcc3213fee4aaf48f2cc065fca7ade98
Reviewed-on: https://skia-review.googlesource.com/c/eskia/+/211577
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
1 file changed