Allow upgrade stream request to be GCd once body has finished

Author: pimterry

lib/_http_server.js

@@ -1019,6 +1019,8 @@ class UpgradeStream extends Duplex {
   }
 
   requestBodyCompleted(upgradeHead) {
+    this[kIncomingMessage] = null;
+
     // When the request body is completed, we begin streaming all the
     // post-body data for the upgraded protocol:
     if (upgradeHead?.length > 0) {
@@ -1039,7 +1041,7 @@ class UpgradeStream extends Duplex {
     // important that this happens, even if there are no listeners, or it
     // would be impossible to read this without explicitly reading all the
     // request body first, which is backward incompatible & awkward.
-    this[kIncomingMessage].resume();
+    this[kIncomingMessage]?.resume();
 
     this[kSocket].resume();
   }