Use two indexes instead of one for hashed urls

When using `OR` in a where clause, a composite index can't be used. We should use a `UNION` to take advantages of it.
Instead, create 2 indexes on each hashed urls and make 2 queries to find an url. It'll be faster than the previous solution.

src/Wallabag/CoreBundle/Entity/Entry.php

@@ -27,7 +27,8 @@ use Wallabag\UserBundle\Entity\User;
  *     indexes={
  *         @ORM\Index(name="created_at", columns={"created_at"}),
  *         @ORM\Index(name="uid", columns={"uid"}),
- *         @ORM\Index(name="hashed_urls_user_id", columns={"user_id", "hashed_url", "hashed_given_url"}, options={"lengths"={null, 40, 40}})
+ *         @ORM\Index(name="hashed_url_user_id", columns={"user_id", "hashed_url"}, options={"lengths"={null, 40}}),
+ *         @ORM\Index(name="hashed_given_url_user_id", columns={"user_id", "hashed_given_url"}, options={"lengths"={null, 40}})
  *     }
  * )
  * @ORM\HasLifecycleCallbacks()

src/Wallabag/CoreBundle/Repository/EntryRepository.php

@@ -366,9 +366,20 @@ class EntryRepository extends EntityRepository
      */
     public function findByHashedUrlAndUserId($hashedUrl, $userId)
     {
+        // try first using hashed_url (to use the database index)
         $res = $this->createQueryBuilder('e')
             ->where('e.hashedUrl = :hashed_url')->setParameter('hashed_url', $hashedUrl)
-            ->orWhere('e.hashedGivenUrl = :hashed_given_url')->setParameter('hashed_given_url', $hashedUrl)
+            ->andWhere('e.user = :user_id')->setParameter('user_id', $userId)
+            ->getQuery()
+            ->getResult();
+
+        if (\count($res)) {
+            return current($res);
+        }
+
+        // then try using hashed_given_url (to use the database index)
+        $res = $this->createQueryBuilder('e')
+            ->where('e.hashedGivenUrl = :hashed_given_url')->setParameter('hashed_given_url', $hashedUrl)
             ->andWhere('e.user = :user_id')->setParameter('user_id', $userId)
             ->getQuery()
             ->getResult();