Fixes #20576

Use-case 1:

import "./foo";

No importClause.name nor importClause.namedBindings, no branch is reached that tries to resolve the module.

Use-case 2:

import {} from "./foo";

No importClause.name, has importClause.namedBindings but it's empty, no branch is reached that tries to resolve the module.

Notes:

1. The only test changed is what seems to have been a false positive.
2. Other tests have their baseline updated, as all new errors thrown are valid and correct, without impairing the underlying test cases as far as I can tell
3. Although the in the issue it is stated use-case 1 is handled correctly by emitting an error, I confirmed in both 2.6.2 and 2.7.0-dev.20171213 that it is not the case.