CheatsManager: Update code tabs on creation

Call `OnStateChanged` when creating CheatsManager to update the AR and
Gecko code tabs with codes for the currently running game (if any).

Previously, creating CheatsManager while a game was running wouldn't
show any codes until the next time the core state changed (excluding
Starting or Stopping which had no effect).

Fixes https://bugs.dolphin-emu.org/issues/13977.

Source/Core/DolphinQt/CheatsManager.cpp

@@ -34,6 +34,8 @@ CheatsManager::CheatsManager(Core::System& system, QWidget* parent)
   CreateWidgets();
   ConnectWidgets();
 
+  OnStateChanged(Core::GetState(system));
+
   QtUtils::AdjustSizeWithinScreen(this);
 
   auto& settings = Settings::GetQSettings();