Try-Catch block added for validation method

Try-catch code block added to validation method. 
This is because application can suffer from errors if there’s no openid inputs on requesting url
I mean,

```php
Route::get('/', function()
{
       $login = new SteamLogin();
       echo $login->validate();
});
```
If I put the following code block to my application route and I request the that url without any paremeter/input. It fails.

That will fix the issue.