SaveState: Fixes from a review of the kernel savestates

- A partition memory block restored its allocator through
  BlockAllocatorFromID, whose privilege check asked the thread current
  before the load, already deleted with the kernel objects. Loading a
  kernel-partition block under a user thread left it without an allocator,
  crashing when it was freed. The saved id maps straight back now, and the
  current thread is cleared along with the objects.
- The thread LoadExec leaves waiting (with no timeout) for plugins and VSH
  modules to start wasn't saved, so a state saved while one was starting
  hung the game thread after loading. The VSH modules still to start
  weren't saved either, nor cleared.
- A state without the exit callback id left the previous session's.
- From a broken or crafted state: thread ids that GetFast trusts (current,
  idle and ready), interrupt handler numbers, FPL and TLSPL indices, and a
  MIPS call or action slot that isn't there.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Core/HLE/sceKernelInterrupt.cpp

@@ -218,6 +218,10 @@ void IntrHandler::DoState(PointerWrap &p)
 
 	Do(p, intrNumber);
 	Do<int, SubIntrHandler>(p, subIntrHandlers);
+	if (p.mode == p.MODE_READ && (intrNumber < 0 || intrNumber >= PSP_NUMBER_INTERRUPTS)) {
+		ERROR_LOG(Log::sceIntc, "Savestate failure: invalid interrupt handler %d", intrNumber);
+		p.SetError(p.ERROR_FAILURE);
+	}
 }
 
 void PendingInterrupt::DoState(PointerWrap &p)