Fix uninitialized g_connman crash in Shutdown()

Author: meshcollider

src/init.cpp

@@ -194,7 +194,7 @@ void Shutdown()
     // Because these depend on each-other, we make sure that neither can be
     // using the other before destroying them.
     UnregisterValidationInterface(peerLogic.get());
-    g_connman->Stop();
+    if(g_connman) g_connman->Stop();
     peerLogic.reset();
     g_connman.reset();