For some unknown reasons, the profiler starts seeing illegal source
positions (see referenced bug).

This CL quick-fixes that by just ignoring them for now. This might
regress profiling, and should be fixed mid-term.

R=mstarzinger@chromium.org

Bug: chromium:953309
Change-Id: I10db7e5ad24e8470e319fc9418cd3a684f614c26
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1569845
Auto-Submit: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60895}