avformat/librtmp: fix swfurl

Found-by: JULIAN GARDNER <joolzg@btinternet.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit d1970929b5)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/librtmp.c

@@ -169,7 +169,7 @@ static int rtmp_open(URLContext *s, const char *uri, int flags)
     }
     if (ctx->swfurl) {
         av_strlcat(filename, " swfUrl=", len);
-        av_strlcat(filename, ctx->pageurl, len);
+        av_strlcat(filename, ctx->swfurl, len);
     }
     if (ctx->flashver) {
         av_strlcat(filename, " flashVer=", len);