change erroneous isResourceArchived return from false to nil

Author: qaisjp

Server/mods/deathmatch/logic/luadefs/CLuaResourceDefs.cpp

@@ -1452,6 +1452,6 @@ int CLuaResourceDefs::isResourceArchived (lua_State* luaVM)
     else
         m_pScriptDebugging->LogCustom(luaVM, argStream.GetFullErrorMessage());
 
-    lua_pushboolean ( luaVM, false );
+    lua_pushnil ( luaVM );
     return 1;
 }