Fix some character sets detection (#1490135)

CHANGELOG

@@ -52,6 +52,7 @@ CHANGELOG Roundcube Webmail
 - Don't remove links when html signature is converted to text (#1489621)
 - Fix page title when using search filter (#1490023)
 - Fix mbox files import
+- Fix some character sets detection (#1490135)
 - Fix so attachment charset is set in headers of forward/draft message (#1490109)
 - Fix bug where wrong charset could be used for text attachment preview page (#1490106)
 - Fix setting flags on servers with no PERMANENTFLAGS response (#1490087)

program/lib/Roundcube/rcube_charset.php

@@ -654,7 +654,6 @@ class rcube_charset
         if ($string[0] == "\0" && $string[1] != "\0" && $string[2] == "\0" && $string[3] != "\0") return 'UTF-16BE';
         if ($string[0] != "\0" && $string[1] == "\0" && $string[2] != "\0" && $string[3] == "\0") return 'UTF-16LE';
 
-        if (function_exists('mb_detect_encoding')) {
         if (empty($language)) {
             $rcube    = rcube::get_instance();
             $language = $rcube->get_user_language();
@@ -682,8 +681,20 @@ class rcube_charset
         case 'tr_TR':
             $prio = array('UTF-8', 'ISO-8859-9', 'WINDOWS-1254');
             break;
+        }
+
+        // mb_detect_encoding() is not reliable for some charsets (#1490135)
+        // use mb_check_encoding() to make charset priority lists really working
+        if ($prio && function_exists('mb_check_encoding')) {
+            foreach ($prio as $encoding) {
+                if (mb_check_encoding($string, $encoding)) {
+                    return $encoding;
+                }
+            }
+        }
 
-            default:
+        if (function_exists('mb_detect_encoding')) {
+            if (!$prio) {
                 $prio = array('UTF-8', 'SJIS', 'GB2312',
                     'ISO-8859-1', 'ISO-8859-2', 'ISO-8859-3', 'ISO-8859-4',
                     'ISO-8859-5', 'ISO-8859-6', 'ISO-8859-7', 'ISO-8859-8', 'ISO-8859-9',
@@ -695,7 +706,9 @@ class rcube_charset
 
             $encodings = array_unique(array_merge($prio, mb_list_encodings()));
 
-            return mb_detect_encoding($string, $encodings);
+            if ($encoding = mb_detect_encoding($string, $encodings)) {
+                return $encoding;
+            }
         }
 
         // No match, check for UTF-8