libavformat/rtpdec_asf: zero initialize the AVIOContext struct

This fixes crash in avformat_open_input() when accessing
protocol_whitelist field.

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit e947b75b1c)

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rtpdec_asf.c

@@ -101,7 +101,7 @@ int ff_wms_parse_sdp_a_line(AVFormatContext *s, const char *p)
 {
     int ret = 0;
     if (av_strstart(p, "pgmpu:data:application/vnd.ms.wms-hdr.asfv1;base64,", &p)) {
-        AVIOContext pb;
+        AVIOContext pb = { 0 };
         RTSPState *rt = s->priv_data;
         AVDictionary *opts = NULL;
         int len = strlen(p) * 6 / 8;