In eval scripts, the source code position can be 0 rather
than greater than 0.

Add regression test.

Drive-by fix: unrelated typo.

Bug: 707223
Change-Id: If52c0736daac3ad42ac6d324eb8ec5f1798f6f5a
Reviewed-on: https://chromium-review.googlesource.com/476630Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Franziska Hinkelmann <franzih@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44637}