General: Convert PanicAlerts over to fmt equivalent

Converts lingering panic alert calls over to the fmt-capable ones.

Source/Core/VideoBackends/Null/NullBackend.cpp

@@ -77,7 +77,7 @@ bool VideoBackend::Initialize(const WindowSystemInfo& wsi)
       !g_renderer->Initialize() || !g_framebuffer_manager->Initialize() ||
       !g_texture_cache->Initialize())
   {
-    PanicAlert("Failed to initialize renderer classes");
+    PanicAlertFmt("Failed to initialize renderer classes");
     Shutdown();
     return false;
   }