fix: Fix undefined function _t on WebSub (#2743)

I published an article via WebSub, but I never received it. So I checked
my logs to find why and I found the following stacktrace:

```
29/Dec/2019:15:58:32 +0000 "POST /api/pshb.php" 500
NOTICE: PHP message: PHP Fatal error:  Uncaught Error: Call to undefined function _t() in /path/app/Models/Category.php:83
Stack trace:
/path/app/Models/CategoryDAO.php(417): FreshRSS_Category->_id(1)
/path/app/Models/CategoryDAO.php(192): FreshRSS_CategoryDAO::daoToCategory(Array)
/path/app/Models/Feed.php(466): FreshRSS_CategoryDAO->searchById('1')
/path/app/Controllers/feedController.php(416): FreshRSS_Feed->cleanOldEntries()
/path/p/api/pshb.php(141): FreshRSS_feed_Controller::actualizeFeed(0, 'https://flus.io...', false, Object(SimplePie))
{main}
  thrown in /path/app/Models/Category.php on line 83
```

The `_t` function should be loaded with the Minz_Translate class, but
the latter isn't initialized on WebSub endpoint.

In my opinion, we should not have to care about this kind of detail of
implementation and it reveals a deeper architectural misconception, but
for now the fix should be enough. It’s quite difficult to reproduce
locally though.

0 files changed, 0 insertions, 0 deletions