MDEV-34976 Server crash report broken if Galera is not loaded

The crash report terminates prematurely when Galera library was
not loaded.

As a fix, check whether the provider is loaded before shutting down
Galera connections.
Signed-off-by: Julius Goryavsky <julius.goryavsky@mariadb.com>

sql/wsrep_server_state.cc

@@ -87,7 +87,7 @@ void Wsrep_server_state::destroy()
 
 void Wsrep_server_state::handle_fatal_signal()
 {
-  if (m_instance)
+  if (m_instance && m_instance->is_provider_loaded())
   {
     /* Galera background threads are still running and the logging may be
        relatively verbose in case of networking error. Silence all wsrep