Fix previous commits not actually nulling out the key

I goofed while porting this from H'uru, where the variable is a
reference. The previous code actually caused the keys to not get deleted
at all.

Sources/Plasma/PubUtilLib/plResMgr/plRegistryKeyList.cpp

@@ -60,7 +60,7 @@ plRegistryKeyList::~plRegistryKeyList()
 	{
 		plKeyImp* keyImp = fStaticKeys[i];
 		if (keyImp && !keyImp->ObjectIsLoaded()) {
-			keyImp = nullptr;
+			fStaticKeys[i] = nullptr;
 			delete keyImp;
 		}
 	}