Validate all text attachments not only text/plain. This fixes invalid

warning message for a case when pdf attachment is defined as text/html.
See #1489267.

program/steps/mail/get.inc

@@ -134,7 +134,7 @@ else if (strlen($part_id)) {
       $valid = $file_extension && in_array($file_extension, (array)$extensions) || !empty($_REQUEST['_mimeclass']);
 
       // 2. detect the real mimetype of the attachment part and compare it with the stated mimetype and filename extension
-      if ($valid || !$file_extension || $mimetype == 'application/octet-stream' || $mimetype == 'text/plain') {
+      if ($valid || !$file_extension || $mimetype == 'application/octet-stream' || stripos($mimetype, 'text/') === 0) {
         if ($part->body)  // part body is already loaded
           $body = $part->body;
         else if ($part->size && $part->size < 1024*1024)   // load the entire part if it's small enough
@@ -233,7 +233,6 @@ else if (strlen($part_id)) {
       header("Content-Transfer-Encoding: binary");
     }
 
-
     // deliver part content
     if ($ctype_primary == 'text' && $ctype_secondary == 'html' && empty($plugin['download'])) {
       // Check if we have enough memory to handle the message in it