PIM-2090 Display error message if launching import without selecting file

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Tests pass?   | yes
| Scenarios pass?   | ?
| Checkstyle issues?  | no
| Changelog updated?  | yes
| Fixed tickets | PIM-2090
| Doc PR        |