src: do not crash when accessing empty WeakRefs

Making `.incRef()` and `.decRef()` fail silently leads to better error
messages when trying to access the underlying value (as opposed to
crashing inside these methods).

Refs: #25461 (comment)

PR-URL: #29289
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Gus Caplan <me@gus.host>

src/node_util.cc

@@ -191,14 +191,16 @@ class WeakReference : public BaseObject {
 
   static void IncRef(const FunctionCallbackInfo<Value>& args) {
     WeakReference* weak_ref = Unwrap<WeakReference>(args.Holder());
-    if (weak_ref->reference_count_ == 0) weak_ref->target_.ClearWeak();
     weak_ref->reference_count_++;
+    if (weak_ref->target_.IsEmpty()) return;
+    if (weak_ref->reference_count_ == 1) weak_ref->target_.ClearWeak();
   }
 
   static void DecRef(const FunctionCallbackInfo<Value>& args) {
     WeakReference* weak_ref = Unwrap<WeakReference>(args.Holder());
     CHECK_GE(weak_ref->reference_count_, 1);
     weak_ref->reference_count_--;
+    if (weak_ref->target_.IsEmpty()) return;
     if (weak_ref->reference_count_ == 0) weak_ref->target_.SetWeak();
   }