fixed debug output, server exit hang, crashes

include/Client.hpp

@@ -61,6 +61,8 @@ public:
 struct ClientInterface{
     std::set<Client*> Clients;
     void RemoveClient(Client *c){
+        Assert(c);
+        c->ClearCars();
         Clients.erase(c);
         delete c;
         c = nullptr;

include/Logger.h

@@ -5,7 +5,6 @@
 #include <iostream>
 #include <mutex>
 #include <string>
-extern std::mutex MLock;
 void InitLog();
 #define DebugPrintTID() DebugPrintTIDInternal(__func__)
 void DebugPrintTIDInternal(const std::string& func); // prints the current thread id in debug mode, to make tracing of crashes and asserts easier