Fix skin extending for assets (#5115)

Remove redundant is_file() calls.

CHANGELOG

@@ -68,6 +68,7 @@ CHANGELOG Roundcube Webmail
 - Handle inline images also inside multipart/mixed messages (#5905)
 - Allow style tags in HTML editor on composed/reply messages (#5751)
 - Use Github API as a fallback to fetch js dependencies to workaround throttling issues (#6248)
+- Fix skin extending for assets (#5115)
 - Fix handling of forwarded messages inside of a TNEF message (#5632)
 - Fix bug where attachment size wasn't visible when the filename was too long (#6033)
 - Fix checking table columns when there's more schemas/databases in postgres/mysql (#6047)

program/include/rcmail_output_html.php

@@ -349,16 +349,12 @@ EOF;
         }
 
         foreach ($skin_paths as $skin_path) {
-            $path = realpath(RCUBE_INSTALL_PATH . $skin_path . $file);
-
-            if ($path && is_file($path)) {
+            if (realpath(RCUBE_INSTALL_PATH . $skin_path . $file)) {
                 return $skin_path . $file;
             }
 
             if ($this->assets_dir != RCUBE_INSTALL_PATH) {
-                $path = realpath($this->assets_dir . $skin_path . $file);
-
-                if ($path && is_file($path)) {
+                if (realpath($this->assets_dir . $skin_path . $file)) {
                     return $skin_path . $file;
                 }
             }
@@ -833,7 +829,8 @@ EOF;
 
         // correct absolute paths
         if ($file[0] == '/') {
-            $file = $this->base_path . $file;
+            $this->get_skin_file($file, $skin_path);
+            $file = $skin_path . $file;
         }
 
         // add file modification timestamp