Regenerate export if missing on view

Thanks to paravibe on Drupal.org for contributing.

h5p-default-storage.class.php

@@ -151,6 +151,17 @@ class H5PDefaultStorage implements \H5PFileStorage {
     }
   }
 
+  /**
+   * Check if the given export file exists
+   *
+   * @param string $filename
+   * @return boolean
+   */
+  public function hasExport($filename) {
+    $target = "{$this->path}/exports/{$filename}";
+    return file_exists($target);
+  }
+
   /**
    * Will concatenate all JavaScrips and Stylesheets into two files in order
    * to improve page performance.

h5p-file-storage.interface.php

@@ -90,6 +90,14 @@ interface H5PFileStorage {
    */
   public function deleteExport($filename);
 
+  /**
+   * Check if the given export file exists
+   *
+   * @param string $filename
+   * @return boolean
+   */
+  public function hasExport($filename);
+
   /**
    * Will concatenate all JavaScrips and Stylesheets into two files in order
    * to improve page performance.

h5p.classes.php

@@ -1812,7 +1812,10 @@ class H5PCore {
    * @return Object NULL on failure.
    */
   public function filterParameters(&$content) {
-    if (isset($content['filtered']) && $content['filtered'] !== '') {
+    if (!empty($content['filtered']) &&
+        (!$this->exportEnabled ||
+         ($content['slug'] &&
+          $this->fs->hasExport($content['slug'] . '-' . $content['id'] . '.h5p')))) {
       return $content['filtered'];
     }