Fix incorrect file attachment if filetype is rejected

If an attachment is submitted via the API and the filetype is rejected, the
file would be attached anyway. However, if the file was encoded base64, the
content would not be decoded.

include/api.tickets.php

@@ -42,7 +42,7 @@ class TicketApiController extends ApiController {
         if($data['attachments'] && is_array($data['attachments'])) {
             foreach($data['attachments'] as &$attachment) {
                 if(!$ost->isFileTypeAllowed($attachment))
-                    $data['error'] = 'Invalid file type (ext) for '.Format::htmlchars($attachment['name']);
+                    $attachment['error'] = 'Invalid file type (ext) for '.Format::htmlchars($attachment['name']);
                 elseif ($attachment['encoding'] && !strcasecmp($attachment['encoding'], 'base64')) {
                     if(!($attachment['data'] = base64_decode($attachment['data'], true)))
                         $attachment['error'] = sprintf('%s: Poorly encoded base64 data', Format::htmlchars($attachment['name']));