fix(core): add missing nullptr check

fix #4324

src/core/core.cpp

@@ -141,8 +141,7 @@ Tox_Options initToxOptions(const QByteArray& savedata)
     toxOptions.proxy_type = TOX_PROXY_TYPE_NONE;
     toxOptions.proxy_host = nullptr;
     toxOptions.proxy_port = 0;
-    toxOptions.savedata_type = !savedata.isNull() ? TOX_SAVEDATA_TYPE_TOX_SAVE
-                                                  : TOX_SAVEDATA_TYPE_NONE;
+    toxOptions.savedata_type = !savedata.isNull() ? TOX_SAVEDATA_TYPE_TOX_SAVE : TOX_SAVEDATA_TYPE_NONE;
     toxOptions.savedata_data = reinterpret_cast<const uint8_t*>(savedata.data());
     toxOptions.savedata_length = savedata.size();
 
@@ -239,6 +238,10 @@ void Core::makeTox(QByteArray savedata)
  */
 void Core::makeAv()
 {
+    if (!tox) {
+        qCritical() << "No Tox instance, can't create ToxAV";
+        return;
+    }
     av = new CoreAV(tox);
     if (!av->getToxAv()) {
         qCritical() << "Toxav core failed to start";
@@ -443,11 +446,7 @@ void Core::onFriendMessage(Tox*, uint32_t friendId, TOX_MESSAGE_TYPE type, const
     emit static_cast<Core*>(core)->friendMessageReceived(friendId, msg, isAction);
 }
 
-void Core::onFriendNameChange(Tox*,
-                              uint32_t friendId,
-                              const uint8_t* cName,
-                              size_t cNameSize,
-                              void* core)
+void Core::onFriendNameChange(Tox*, uint32_t friendId, const uint8_t* cName, size_t cNameSize, void* core)
 {
     QString newName = ToxString(cName, cNameSize).getQString();
     emit static_cast<Core*>(core)->friendUsernameChanged(friendId, newName);
@@ -1470,7 +1469,9 @@ void Core::setNospam(uint32_t nospam)
 void Core::killTimers(bool onlyStop)
 {
     assert(QThread::currentThread() == coreThread);
-    av->stop();
+    if (av) {
+        av->stop();
+    }
     toxTimer->stop();
     if (!onlyStop) {
         delete toxTimer;