Prevent trying to access an entry when none exist.

[Kurochi51]

I'm not quite sure what's the root cause, but I noticed this error gets spammed in the very first few seconds of the game launching post-injection.

[ERR] [WindowSystem] Error during Draw(): TitleScreenMenuOverlay
System.ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection. (Parameter 'index')
at System.SZArrayHelper.get_Item[T](Int32 index)
at Dalamud.Interface.Internal.Windows.TitleScreenMenuWindow.Draw() in C:\goatsoft\companysecrets\dalamud\Interface\Internal\Windows\TitleScreenMenuWindow.cs:line 273
at Dalamud.Interface.Windowing.Window.DrawInternal(DalamudConfiguration configuration) in C:\goatsoft\companysecrets\dalamud\Interface\Windowing\Window.cs:line 346

It seems to be because this.titleScreenMenu.PluginEntries is empty, although I didn't notice a behaviour change when this was changed in #1808, so I'm unsure if it's a coincidence, or a side effect of the many changes that happened recently.