Fix use of unitialized value in test

Local media SSRC is mandatory, but let's give it a default value to
make tests less brittle.

Bug: chromium:1015256
Change-Id: If7f6505482d90651bc58d9b358290c4d43487f4e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/157421
Commit-Queue: Erik Språng <sprang@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29534}

modules/rtp_rtcp/include/rtp_rtcp.h

@@ -123,7 +123,7 @@ class RtpRtcp : public Module, public RtcpFeedbackSenderInterface {
 
     // SSRCs for media and retransmission, respectively.
     // FlexFec SSRC is fetched from |flexfec_sender|.
-    uint32_t local_media_ssrc;
+    uint32_t local_media_ssrc = 0;
     absl::optional<uint32_t> rtx_send_ssrc;
 
    private:

test/fuzzers/rtcp_receiver_fuzzer.cc

@@ -43,6 +43,7 @@ void FuzzOneInput(const uint8_t* data, size_t size) {
   RtpRtcp::Configuration config;
   config.clock = &clock;
   config.rtcp_report_interval_ms = kRtcpIntervalMs;
+  config.local_media_ssrc = 1;
 
   RTCPReceiver receiver(config, &rtp_rtcp_module);