fix(client): only take single url on (args.resume && first)

QUIC Interop Runner testcases `resumption` and `0-rtt` expect the client to
download the first file, close the connection, and then download the remaining
files on a second connection.

https://github.com/quic-interop/quic-interop-runner/tree/master#test-cases

Thus `neqo-client`, when `args.resume` is `true` must only take a single URL on
the **first** loop iteration. On the second iteration it must take all remaining
URLs.

Regression introduced in mozilla#1569.

neqo-client/src/main.rs

@@ -1086,13 +1086,16 @@ fn main() -> Res<()> {
 
         let hostname = format!("{host}");
         let mut token: Option<ResumptionToken> = None;
+        let mut first = true;
         while !urls.is_empty() {
-            let to_request = if args.resume || args.download_in_series {
+            let to_request = if (args.resume && first) || args.download_in_series {
                 urls.pop_front().into_iter().collect()
             } else {
                 std::mem::take(&mut urls)
             };
 
+            first = false;
+
             token = if args.use_old_http {
                 old::old_client(
                     &args,