[BUG] [CRASH] Segmentation Fault in Phalcon\Tag::setDI() and setDefaults()

Similar to #741

Test case:
```php
<?php
$v = new Phalcon\Tag;
try {
        $v->setDI(new Phalcon\Di()); // segfault
}
catch (Exception $e) {
        echo "Exception caught!\n";
}

try {
        $v->setDefaults(0);
}
catch (Exception $e) {
        echo "Exception caught!\n"; // segfault
}
```