MDL-58823 repository: Fix redirections to external files

We cannot use redirect() because is not compatible with
webservice/pluginfile.php
This script is defined as an AJAX_SCRIPT so redirections are not
allowed by redirect() function.

repository/filesystem/lib.php

@@ -845,7 +845,8 @@ function repository_filesystem_pluginfile($course, $cm, $context, $filearea, $ar
     // Find stored or generated thumbnail.
     if (!($file = $repo->get_thumbnail($filepath, $filearea))) {
         // Generation failed, redirect to default icon for file extension.
-        redirect($OUTPUT->image_url(file_extension_icon($file, 90)));
+        // Do not use redirect() here because is not compatible with webservice/pluginfile.php.
+        header('Location: ' . $OUTPUT->image_url(file_extension_icon($file, 90)));
     }
     // The thumbnails should not be changing much, but maybe the default lifetime is too long.
     $lifetime = $CFG->filelifetime;

repository/googledocs/lib.php

@@ -630,7 +630,8 @@ class repository_googledocs extends repository {
             }
             send_file($downloaded['path'], $filename, $lifetime, $filter, false, $forcedownload, '', false, $options);
         } else if ($source->link) {
-            redirect($source->link);
+            // Do not use redirect() here because is not compatible with webservice/pluginfile.php.
+            header('Location: ' . $source->link);
         } else {
             $details = 'File is missing source link';
             throw new repository_exception('errorwhilecommunicatingwith', 'repository', '', $details);

repository/onedrive/lib.php

@@ -577,7 +577,8 @@ class repository_onedrive extends repository {
             $filename = $storedfile->get_filename();
             send_file($downloaded['path'], $filename, $lifetime, $filter, false, $forcedownload, '', false, $options);
         } else if ($source->link) {
-            redirect($source->link);
+            // Do not use redirect() here because is not compatible with webservice/pluginfile.php.
+            header('Location: ' . $source->link);
         } else {
             $details = 'File is missing source link';
             throw new repository_exception('errorwhilecommunicatingwith', 'repository', '', $details);