Ensure pipeTo() releases its reader correctly

The user agent is allowed to use a default reader or a BYOB reader for the pipe, but we were always calling ReadableStreamDefaultReaderRelease in the finalize steps. This commit fixes the algorithm to we should use the appropriate release abstract operation corresponding to the chosen reader.

This was broken in d5f92d9.

index.bs

@@ -2219,7 +2219,9 @@ The following abstract operations operate on {{ReadableStream}} instances at a h
   * <dfn id="rs-pipeTo-finalize"><i>Finalize</i></dfn>: both forms of shutdown will eventually ask
     to finalize, optionally with an error |error|, which means to perform the following steps:
    1. Perform ! [$WritableStreamDefaultWriterRelease$](|writer|).
-   1. Perform ! [$ReadableStreamDefaultReaderRelease$](|reader|).
+   1. If |reader| [=implements=] {{ReadableStreamBYOBReader}}, perform
+      ! [$ReadableStreamBYOBReaderRelease$](|reader|).
+   1. Otherwise, perform ! [$ReadableStreamDefaultReaderRelease$](|reader|).
    1. If |signal| is not undefined, [=AbortSignal/remove=] |abortAlgorithm| from |signal|.
    1. If |error| was given, [=reject=] |promise| with |error|.
    1. Otherwise, [=resolve=] |promise| with undefined.