Disable logging on static instance destruction.

This avoids possible deadlocks on exit when a logger callback exists.

src/Dispatcher.cpp

@@ -43,6 +43,7 @@ DispatcherBase::DispatcherBase(Storage& storage, Notifier& notifier)
 }
 
 DispatcherBase::~DispatcherBase() {
+  Logger::GetInstance().SetLogger(nullptr);
   Stop();
 }
 

src/RpcServer.cpp

@@ -19,6 +19,7 @@ RpcServer::RpcServer() {
 }
 
 RpcServer::~RpcServer() {
+  Logger::GetInstance().SetLogger(nullptr);
   Stop();
   m_terminating = true;
   m_poll_cond.notify_all();

src/Storage.cpp

@@ -29,6 +29,7 @@ Storage::Storage(Notifier& notifier, RpcServer& rpc_server)
 }
 
 Storage::~Storage() {
+  Logger::GetInstance().SetLogger(nullptr);
   m_terminating = true;
   m_rpc_results_cond.notify_all();
 }