http_streamer: don't access headers before HeadersReceived.

UpdateSize uses HttpResult::Length, which relies on the
contetn-length header to be already received from the server. Doing it
in ConnectionOpened will not work. Doing it from HeadersReceived, which
is called a bit later, will work.

This allows using the http_streamer in webkit for youtube video playing,
and should fix all uses with a fixed size resource (rather than an
endless stream).

src/add-ons/media/plugins/http_streamer/HTTPMediaIO.cpp

@@ -43,12 +43,15 @@ public:
 
 		void ConnectionOpened(BUrlRequest* request)
 		{
-			fAdapterIO->UpdateSize();
-
 			fRequest = request;
 			fRunning = true;
 		}
 
+		void HeadersReceived(BUrlRequest* request)
+		{
+			fAdapterIO->UpdateSize();
+		}
+
 		void DataReceived(BUrlRequest* request, const char* data,
 			off_t position, ssize_t size)
 		{