getSortByDomain throws error on file:/// URLs

[diracdeltas]

Test plan

#8969 (comment)

---

STR:
open a file URL
go to a new tab, type fi in the urlbar
console shows error:

An uncaught exception occurred in the main process Uncaught Exception:
TypeError: Cannot read property 'indexOf' of null
    at /Users/yan/repos/browser-laptop/app/common/lib/suggestion.js:241:21
    at /Users/yan/repos/browser-laptop/app/common/lib/suggestion.js:343:34
    at /Users/yan/repos/browser-laptop/node_modules/immutable/dist/immutable.js:3481:42
    at Array.sort (native)
    at sortFactory (/Users/yan/repos/browser-laptop/node_modules/immutable/dist/immutable.js:3481:13)
    at List.sort (/Users/yan/repos/browser-laptop/node_modules/immutable/dist/immutable.js:4444:26)
    at /Users/yan/repos/browser-laptop/app/common/lib/suggestion.js:393:6
    at query.then (/Users/yan/repos/browser-laptop/app/common/lib/suggestion.js:419:31)
    at <anonymous>

on master