Update the DB output hash if outdated according to texvc

* Otherwise all future <math> hits will check the wrong file
  (which may not exist), recreate the png, and store over the
  proper file (even if it was already there). Update the DB to
  point to the right hash instead.

bug: 60997
Change-Id: Ib833ad32ff1e4506e9b8ab2cc1b72516cb072cd5
(cherry picked from commit 078347b35e10cfdc54c400c4752fd4d6d8fb021b)