Revision 5bc1d291 introduced a bug in the case when the filler is in
the unmapped region, which leads to CHECK failure.

Change-Id: I013e4386f6d5e9cdad22c11e1a7a9f1a088375ae
Reviewed-on: https://chromium-review.googlesource.com/823845Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50080}