Return the user id in case of an error

Signed-off-by: Joas Schilling <coding@schilljs.com>

core/Controller/AvatarController.php

@@ -143,7 +143,7 @@ class AvatarController extends Controller {
 		} catch (\Exception $e) {
 			$resp = new JSONResponse([
 				'data' => [
-					'displayname' => '',
+					'displayname' => $userId,
 				],
 			]);
 		}

tests/Core/Controller/AvatarControllerTest.php

@@ -169,7 +169,7 @@ class AvatarControllerTest extends \Test\TestCase {
 		//Comment out until JS is fixed
 		//$this->assertEquals(Http::STATUS_NOT_FOUND, $response->getStatus());
 		$this->assertEquals(Http::STATUS_OK, $response->getStatus());
-		$this->assertEquals('', $response->getData()['data']['displayname']);
+		$this->assertEquals('userDoesNotExist', $response->getData()['data']['displayname']);
 	}
 
 	/**