Fix potential crash because of the call statistics, the payload type returned...

Fix potential crash because of the call statistics, the payload type returned by getUsedAudioCodec() and getUsedVideoCodec() may be null.

linphone-desktop/src/components/call/CallModel.cpp

@@ -456,8 +456,8 @@ void CallModel::updateStats (const linphone::CallStats &callStats, QVariantList
 
   stats.clear();
 
-  stats << createStat(tr("callStatsCodec"), QString("%1 / %2kHz")
-    .arg(Utils::linphoneStringToQString(payloadType->getMimeType())).arg(payloadType->getClockRate() / 1000));
+  stats << createStat(tr("callStatsCodec"), payloadType ? QString("%1 / %2kHz")
+    .arg(Utils::linphoneStringToQString(payloadType->getMimeType())).arg(payloadType->getClockRate() / 1000) : "");
   stats << createStat(tr("callStatsUploadBandwidth"), QString("%1 kbits/s").arg(int(callStats.getUploadBandwidth())));
   stats << createStat(tr("callStatsDownloadBandwidth"), QString("%1 kbits/s").arg(int(callStats.getDownloadBandwidth())));
   stats << createStat(tr("callStatsIceState"), iceStateToString(callStats.getIceState()));