Small fixes

[Cimbali]

I was going over the code to look at writing up some PRs and stumbled across 2 small easily corrected issues:

• a Promise’s resolve() being called twice, which is meaningless.
  Note that I’ve checked that using else for fallback/function exit is OK per style, see e.g.

  multi-account-containers/src/js/background/assignManager.js

  Lines 16 to 20 in 60b40a2

  	if (url.port === "80" || url.port === "443") {
  	return `${storagePrefix}${url.hostname}`;
  	} else {
  	return `${storagePrefix}${url.hostname}${url.port}`;
  	}

• A function call to getByContainer() which doesn’t exist (there is a getAssignedSites() which in turn calls _getByContainer())