Also guard against accessing plRegistryKeyList currently being deleted

Co-authored-by: Adam Johnson <AdamJohnso@gmail.com>

(ported from H-uru/Plasma@725eeaa28820423f8f36e3476d0f5c6da30921c2)

Sources/Plasma/PubUtilLib/plResMgr/plRegistryKeyList.cpp

@@ -60,8 +60,8 @@ plRegistryKeyList::~plRegistryKeyList()
 	{
 		plKeyImp* keyImp = fStaticKeys[i];
 		if (keyImp && !keyImp->ObjectIsLoaded()) {
-			delete keyImp;
 			keyImp = nullptr;
+			delete keyImp;
 		}
 	}
 }

Sources/Plasma/PubUtilLib/plResMgr/plRegistryNode.cpp

@@ -203,8 +203,8 @@ void plRegistryPageNode::UnloadKeys()
 	for (; it != fKeyLists.end(); it++)
 	{
 		plRegistryKeyList* keyList = it->second;
-		delete keyList;
 		it->second = nullptr;
+		delete keyList;
 	}
 	fKeyLists.clear();