fixes #14402 (#14908)

* fixes #14402

* added a test case

lib/pure/asyncstreams.nim

@@ -96,7 +96,7 @@ proc read*[T](future: FutureStream[T]): owned(Future[(bool, T)]) =
       if resFut.finished: return
 
       # We don't want this callback called again.
-      future.cb = nil
+      #future.cb = nil
 
       # The return value depends on whether the FutureStream has finished.
       var res: (bool, T)

tests/arc/tasyncorc.nim

@@ -0,0 +1,26 @@
+discard """
+  output: '''230000'''
+  cmd: '''nim c --gc:orc -d:useMalloc $file'''
+  valgrind: "true"
+"""
+
+# bug #14402
+
+import asynchttpserver, asyncdispatch, httpclient, strutils
+
+proc cb(req: Request) {.async, gcsafe.} =
+  const html = " ".repeat(230000)
+  await req.respond(Http200, html)
+
+var server = newAsyncHttpServer()
+asyncCheck server.serve(Port(8080), cb)
+
+proc test {.async.} =
+  var
+    client = newAsyncHttpClient()
+    resp = await client.get("http://localhost:8080")
+
+  let x = (await resp.body).len
+  echo x # crash
+
+waitFor test()