Validate imported entry to avoid error on import

We got some imports with a missing `url` field generating some errors while trying to retrieve an existing entry with that url.
Introducing the `validateEntry` allow us to dismiss a message when it doesn't have an url (or other missing stuff in the future)

src/Wallabag/ImportBundle/Import/AbstractImport.php

@@ -118,6 +118,15 @@ abstract class AbstractImport implements ImportInterface
      */
     abstract public function parseEntry(array $importedEntry);
 
+    /**
+     * Validate that an entry is valid (like has some required keys, etc.).
+     *
+     * @param array $importedEntry
+     *
+     * @return bool
+     */
+    abstract public function validateEntry(array $importedEntry);
+
     /**
      * Fetch content from the ContentProxy (using graby).
      * If it fails return the given entry to be saved in all case (to avoid user to loose the content).
@@ -141,9 +150,9 @@ abstract class AbstractImport implements ImportInterface
     /**
      * Parse and insert all given entries.
      *
-     * @param $entries
+     * @param array $entries
      */
-    protected function parseEntries($entries)
+    protected function parseEntries(array $entries)
     {
         $i = 1;
         $entryToBeFlushed = [];
@@ -153,6 +162,10 @@ abstract class AbstractImport implements ImportInterface
                 $importedEntry = $this->setEntryAsRead($importedEntry);
             }
 
+            if (false === $this->validateEntry($importedEntry)) {
+                continue;
+            }
+
             $entry = $this->parseEntry($importedEntry);
 
             if (null === $entry) {