Add a virtual destructor to http_server_base

Clang warns about http_server having a non-virtual destructor; we aren't
actually doing anything that would cause problems, but the warning is
legit and a correct thing to fix.

src/rpc/http_server.h

@@ -63,7 +63,7 @@ namespace cryptonote::rpc {
         std::vector<std::tuple<std::string, uint16_t, bool>> bind // {IP,port,required}
         );
 
-    ~http_server();
+    ~http_server() override;
 
     /// Starts the event loop in the thread handling http requests.  Core must have been initialized
     /// and OxenMQ started.  Will propagate an exception from the thread if startup fails.

src/rpc/http_server_base.h

@@ -64,6 +64,8 @@ namespace cryptonote::rpc {
 
   protected:
 
+    virtual ~http_server_base() = default;
+
     virtual void create_rpc_endpoints(uWS::App& http) = 0;
 
     /// handles cors headers by adding any needed headers to the given vector