Guard item.original write in HookingSystem::Detach

[JustinMDotNet]

Closes #136.

What this changes

HookingSystem::Detach now guards the write to item.original with a null check, the same way Attach already does:

if (item.original)
{
    *item.original = nullptr;
}
it = m_hooks.erase(it);

Why

HookingSystem::Attach treats aOriginal as optional (it only writes through it when it is non-null, see HookingSystem.cpp:64), and the v1 entry point in Funcs.cpp:40-44 only rejects null aTarget and aDetour — aOriginal is allowed to be null. But the previous Detach did *item.original = nullptr; unconditionally, so any plugin that legitimately registered a hook without asking for the original trampoline would crash the game process the first time it removed that hook.

Reproducer:

sdk->hooking->Attach(handle, target, detour, nullptr);
sdk->hooking->Detach(handle, target);   // <-- AV inside HookingSystem

HookingSystem::Shutdown is not affected because it uses QueueForDetach + m_hooks.clear() and never writes through item.original.

What I tested

Local rebuild. Behavior change is limited to the aOriginal == nullptr path, which previously always crashed; for plugins that passed a non-null aOriginal the behavior is identical.

Alternative considered

Rejecting aOriginal == nullptr at the v1 boundary in Funcs.cpp::v1::Hooking::Attach. That is a contract change and breaks the symmetry with Attach's existing optional-out behavior, so I went with the guard. Happy to switch to the boundary check if you would prefer.