Fix EZP-23477: exception when trashing empty iumage

> Fixes [EZP-23477]()

```
Argument 'BinaryFile::id' is invalid: '' is wrong value in class 'BinaryFile'
```
Fixed by only calling `ezpEvent::getInstance()->notify( 'image/trashAliases', array( $originalAlias['url'] ) );` if there is an actual image to trash aliases for.