multi search now response 404 properly

Author: Mpdreamz

src/Tests/Search/MultiSearch/MultiSearchInvalidApiTests.cs

@@ -77,8 +77,9 @@ [I] public Task AssertResponse() => AssertOnAllResponses(r =>
 		private void AssertInvalidResponse(IResponse searchResponse)
 		{
 			searchResponse.ShouldNotBeValid();
+
 			searchResponse.ServerError.Should().NotBeNull();
-			searchResponse.ServerError.Status.Should().Be(-1);
+			searchResponse.ServerError.Status.Should().Be(404);
 			searchResponse.ServerError.Error.Should().NotBeNull();
 			searchResponse.ServerError.Error.Type.Should().Be("index_not_found_exception");
 			searchResponse.ServerError.Error.Reason.Should().Be("no such index");