SkSplicer: always initialize fLowp

SkSplicer: always initialize fLowp

UBSAN sees copying non-bool (uninitialized) values into this bool.  Not
really a big deal, as we'll never actually use it in that case, but it's
best to just initialize it to true or false.

Change-Id: I38137d46a8aa6e6651325002b71ae5e33ff24c4a
Reviewed-on: https://skia-review.googlesource.com/7321
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>