Update Lua callback check in file config

Modified the HaveLuaCallback function in file.go to use the GetConfig function for validating the callback script. This new implementation provides an additional null check to avoid potential null-pointer exceptions, increasing the robustness of the function.

Signed-off-by: Christian Roessner <c@roessner.co>

server/config/file.go

@@ -533,7 +533,12 @@ func (f *File) HaveLuaActions() bool {
 
 func (f *File) HaveLuaCallback() bool {
 	if f.HaveLua() {
-		return f.Lua.Config.CallbackScriptPath != ""
+		getConfig := f.GetConfig(global.BackendLua)
+		if getConfig == nil {
+			return false
+		}
+
+		return getConfig.(*LuaConf).CallbackScriptPath != ""
 	}
 
 	return false