[Svn] [roundcube/roundcubemail] ecde98: Fix skin extending for assets (#5115)

[GitHub]

  Branch: refs/heads/master
  Home:   https://github.com/roundcube/roundcubemail
  Commit: ecde98729becf84652783cd90f368d453f80edee
      https://github.com/roundcube/roundcubemail/commit/ecde98729becf84652783cd90f368d453f80edee
  Author: Aleksander Machniak <alec at alec.pl>
  Date:   2018-04-15 (Sun, 15 Apr 2018)

  Changed paths:
    M CHANGELOG
    M program/include/rcmail_output_html.php

  Log Message:
  -----------
  Fix skin extending for assets (#5115)

Remove redundant is_file() calls.