Router errors on queries that contains only __typename on root level that wrapped in fragment

[IvanGoncharov]

Describe the bug

Queries like { __typename } works on router but if you wrap it in fragment like this { ... { __typename } } it produces an error:

value retrieval failed: empty query plan. This behavior is unexpected and we suggest opening an issue to apollographql/router with a reproduction.

To Reproduce

See test cases here:

router/apollo-router/tests/integration/typename.rs

Lines 74 to 138 in 7402a1b

	/* FIXME: should be fixed in query planner, failing with:
	> value retrieval failed: empty query plan. This behavior is unexpected and we suggest opening an issue to apollographql/router with a reproduction.
	#[tokio::test]
	async fn inside_inline_fragment() {
	let request = Request::fake_builder()
	.query("{ ... { __typename } }")
	.build()
	.unwrap();
	let response = make_request(request).await;
	insta::assert_json_snapshot!(response, @r###"
	{
	"data": {
	"n": "MyQuery"
	}
	}
	"###);
	}
	#[tokio::test]
	async fn inside_fragment() {
	let query = r#"
	{ ...SomeFragment }
	fragment SomeFragment on MyQuery {
	__typename
	}
	"#;
	let request = Request::fake_builder().query(query).build().unwrap();
	let response = make_request(request).await;
	insta::assert_json_snapshot!(response, @r###"
	{
	"data": {
	"n": "MyQuery"
	}
	}
	"###);
	}
	#[tokio::test]
	async fn deeply_nested_inside_fragments() {
	let query = r#"
	{ ...SomeFragment }
	fragment SomeFragment on MyQuery {
	... {
	...AnotherFragment
	}
	}
	fragment AnotherFragment on MyQuery {
	__typename
	}
	"#;
	let request = Request::fake_builder().query(query).build().unwrap();
	let response = make_request(request).await;
	insta::assert_json_snapshot!(response, @r###"
	{
	"data": {
	"n": "MyQuery"
	}
	}
	"###);
	}
	*/