don't attempt to set the i18n scope if the template has no virtual path

this ensures 404 pages don't result in 500 pages

test plan:
1. go to /assets/common_legacy_normal_contrast.js
2. you should see a 404 page instead of a 500 page

Change-Id: I710c05fdf97b6f5ff337706798cad415fedc4bc3
Reviewed-on: https://gerrit.instructure.com/39570
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Jon Jensen <jon@instructure.com>