Fix displaying attached images with wrong Content-Type specified (#5527)

CHANGELOG

@@ -15,6 +15,7 @@ CHANGELOG Roundcube Webmail
 - Fix "Illegal string offset" warning in rcube::log_bug() on PHP 7.1 (#5508)
 - Fix storing "empty" values in rcube_cache/rcube_cache_shared (#5519)
 - Fix missing content check when image resize fails on attachment thumbnail generation (#5485)
+- Fix displaying attached images with wrong Content-Type specified (#5527)
 
 RELEASE 1.2.2
 -------------

program/steps/mail/get.inc

@@ -180,6 +180,10 @@ if (strlen($part_id)) {
                 if ($mimetype == 'application/octet-stream' && strpos($real_mimetype, 'image/') === 0 && $valid_extension) {
                     $mimetype = $real_mimetype;
                 }
+                // fix mimetype for images with wrong mimetype
+                else if (strpos($real_mimetype, 'image/') === 0 && strpos($mimetype, 'image/') === 0) {
+                    $mimetype = $real_mimetype;
+                }
 
                 // "fix" real mimetype the same way the original is before comparison
                 $real_mimetype = rcmail_fix_mimetype($real_mimetype);
@@ -226,7 +230,6 @@ if (strlen($part_id)) {
             }
         }
 
-
         // TIFF to JPEG conversion, if needed
         $tiff_support = !empty($_SESSION['browser_caps']) && !empty($_SESSION['browser_caps']['tif']);
         if (!empty($_REQUEST['_embed']) && !$tiff_support