Shared/Metric: Fix crash on shutdown

Fix crash on shutdown with metrics enabled but InfluxDB stopping before worldserver

(cherry picked from commit 45b2bcfaf2)

src/server/worldserver/Main.cpp

@@ -243,7 +243,7 @@ extern int main(int argc, char** argv)
     std::shared_ptr<void> sMetricHandle(nullptr, [](void*)
     {
         TC_METRIC_EVENT("events", "Worldserver shutdown", "");
-        sMetric->ForceSend();
+        sMetric->Unload();
     });
 
     sScriptMgr->SetScriptLoader(AddScripts);