Throw exception if addTrack() is called when the transport is not initialized (instead of ignoring it)

src/impl/peerconnection.cpp

@@ -758,9 +758,17 @@ void PeerConnection::openTracks() {
 #if RTC_ENABLE_MEDIA
 	if (auto transport = std::atomic_load(&mDtlsTransport)) {
 		auto srtpTransport = std::dynamic_pointer_cast<DtlsSrtpTransport>(transport);
-		iterateTracks([&](shared_ptr<Track> track) {
-			if (!track->isOpen())
-				track->open(srtpTransport);
+
+		iterateTracks([&](const shared_ptr<Track>& track) {
+			if (!track->isOpen()) {
+				if (srtpTransport) {
+					track->open(srtpTransport);
+				} else {
+					auto errorMsg = "addTrack() was called, but srtp transport was not initialized. This is an optimization for use of the library with data channels only. Set config.forceMediaTransport to 'true' to get the transport initialized before dynamically adding tracks.";
+					PLOG_ERROR << errorMsg;
+					track->triggerError(errorMsg);
+				}
+			}
 		});
 	}
 #endif