DevTools: fix bug in "goto source" fuzzy matching

The patch eliminates a bug that caused algorithm to accidentally
truncate match sequences.

BUG=410194
R=vsevik

Review URL: https://codereview.chromium.org/663423002

git-svn-id: svn://svn.chromium.org/blink/trunk@184096 bbb929c8-8fbe-4397-9dbb-9b2b20218538