Fix false warning when opening attached text/plain files (#1490241)

CHANGELOG

@@ -15,6 +15,7 @@ CHANGELOG Roundcube Webmail
 - Fix bug where empty fieldmap config entries caused empty results of ldap search (#1490229)
 - Fix bug where drafts list wasn't refreshed after draft message was sent from another window (#1490238)
 - Fix keyboard navigation and css in datepicker widget across many Firefox versions
+- Fix false warning when opening attached text/plain files (#1490241)
 
 RELEASE 1.1-rc
 --------------

program/steps/mail/get.inc

@@ -150,22 +150,22 @@ else if (strlen($part_id)) {
 
                 // accept text/plain with any extension
                 if ($real_mimetype == 'text/plain' && $real_mimetype == $mimetype) {
-                    $file_extension = 'txt';
+                    $valid_extension = true;
                 }
-
                 // ignore differences in text/* mimetypes. Filetype detection isn't very reliable here
-                if ($real_ctype_primary == 'text' && strpos($mimetype, $real_ctype_primary) === 0) {
-                    $real_mimetype = $mimetype;
+                else if ($real_ctype_primary == 'text' && strpos($mimetype, $real_ctype_primary) === 0) {
+                    $real_mimetype   = $mimetype;
+                    $valid_extension = true;
                 }
-
-                // get valid file extensions
-                $extensions      = rcube_mime::get_mime_extensions($real_mimetype);
-                $valid_extension = (!$file_extension || in_array($file_extension, (array)$extensions));
-
                 // ignore filename extension if mimeclass matches (#1489029)
-                if (!empty($_REQUEST['_mimeclass']) && $real_ctype_primary == $_REQUEST['_mimeclass']) {
+                else if (!empty($_REQUEST['_mimeclass']) && $real_ctype_primary == $_REQUEST['_mimeclass']) {
                     $valid_extension = true;
                 }
+                else {
+                    // get valid file extensions
+                    $extensions      = rcube_mime::get_mime_extensions($real_mimetype);
+                    $valid_extension = (!$file_extension || in_array($file_extension, (array)$extensions));
+                }
 
                 // fix mimetype for images wrongly declared as octet-stream
                 if ($mimetype == 'application/octet-stream' && strpos($real_mimetype, 'image/') === 0 && $valid_extension) {