Don't log parsing error when trying to parse a missing .po file

[flodolo]

Currently we have a lot of warnings from foundation-website-content, where a .po file is missing we apparently try to parse them, and generate an error.

[Sep 14 07:08:39](https://papertrailapp.com/heroku/go/84610504?a=app36168353&app=mozilla-pontoon&centered_on_id=1506602792355569691&search_id=123759891) mozilla-pontoon app/worker.1: Skipping resource pages/homepage/blog/reporting-back-on-mozillas-cryptocurrency-donation-policy.po due to ParseError: Failed to parse /app/media/projects/foundation-website-content/[email protected]:mozilla-l10n/fomo-content.git/locales/sw/pages/homepage/blog/reporting-back-on-mozillas-cryptocurrency-donation-policy.po: Syntax error in po file None (line 1)

The file in question doesn't exist.

[flodolo]

@mathjazz Is this what you were thinking?