Add the file extension on to the filename if it is missing

This is required within the upload logic of wordpress to determine the mimetype, and whether to allow the file to be uploaded

Files without this extension fail this validation check.

includes/classes/sync/pull.php

@@ -10,6 +10,7 @@
 
 use GatherContent\Importer\Mapping_Post;
 use GatherContent\Importer\API;
+use Mimey\MimeTypes;
 use WP_Error;
 
 /**
@@ -881,6 +882,12 @@ protected function maybe_sideload_file( $media, $post_id ) {
 	protected function sideload_file( $file_name, $download_url, $post_id, $alt_text = '' ) {
 		if ( ! empty( $download_url ) ) {
 			$file_array = $this->tmp_file( $file_name, $download_url );
+			$file_array['type'] = mime_content_type($file_array['tmp_name']);
+			$extension = '.' . (new MimeTypes())->getExtension($file_array['type']);
+			$hasExtension = substr($file_array['name'], 0 - strlen($extension)) === $extension;
+			if (!$hasExtension) {
+				$file_array['name'] = $file_array['name'] . $extension;
+			}
 
 			if ( is_wp_error( $file_array ) ) {
 				return $file_array;