BUG/MINOR: stream: Don't use input buffer after the ownership xfer

At the end of stream_new(), once the input buffer is transfer to the request
channel, it must not be used anymore. The previous patch (16df178b6 "BUG/MEDIUM:
stream: Xfer the input buffer to a fully created stream") was pushed to quickly.

No backport needed.
diff --git a/src/stream.c b/src/stream.c
index 14138f0..690fe3e 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -526,7 +526,7 @@
 		 */
 		s->req.buf = *input;
 		*input = BUF_NULL;
-		s->req.total = (IS_HTX_STRM(s) ? htxbuf(input)->data : b_data(input));
+		s->req.total = (IS_HTX_STRM(s) ? htxbuf(&s->req.buf)->data : b_data(&s->req.buf));
 		s->req.flags |= (s->req.total ? CF_READ_PARTIAL : 0);
 	}