avformat/rtsp: Check that lower transport is handled in one of the if()

Fixes: CID1473554 Uninitialized scalar variable

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit c8200d3825)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/rtsp.c

@@ -1576,7 +1576,11 @@ int ff_rtsp_make_setup_request(AVFormatContext *s, const char *host, int port,
         else if (lower_transport == RTSP_LOWER_TRANSPORT_UDP_MULTICAST) {
             snprintf(transport, sizeof(transport) - 1,
                      "%s/UDP;multicast", trans_pref);
+        } else {
+            err = AVERROR(EINVAL);
+            goto fail; // transport would be uninitialized
         }
+
         if (s->oformat) {
             av_strlcat(transport, ";mode=record", sizeof(transport));
         } else if (rt->server_type == RTSP_SERVER_REAL ||