Curl_read: check for activated HTTP/1 pipelining, not only requested

... as when pipelining is used, we read things into a unified buffer and
we don't do that with HTTP/2. This could then easily make programs that
set CURLMOPT_PIPELINING = CURLPIPE_HTTP1|CURLPIPE_MULTIPLEX to get data
intermixed or plain broken between HTTP/2 streams.

Reported-by: Anders Bakken

lib/sendf.c

@@ -5,7 +5,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2015, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2016, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -553,7 +553,10 @@ CURLcode Curl_read(struct connectdata *conn, /* connection data */
   ssize_t nread = 0;
   size_t bytesfromsocket = 0;
   char *buffertofill = NULL;
-  bool pipelining = Curl_pipeline_wanted(conn->data->multi, CURLPIPE_HTTP1);
+
+  /* if HTTP/1 pipelining is both wanted and possible */
+  bool pipelining = Curl_pipeline_wanted(conn->data->multi, CURLPIPE_HTTP1) &&
+    (conn->bundle->multiuse == BUNDLE_PIPELINING);
 
   /* Set 'num' to 0 or 1, depending on which socket that has been sent here.
      If it is the second socket, we set num to 1. Otherwise to 0. This lets