FIx wrong path creation in css pack

[Alexnder]

If you have several files of one font, for ex.: url(fonts/font.woff) url(fonts/font.woff2) It's pack to this:

url(/design/siteaccess/stylesheets/fonts/font.woff)
url(/design/siteaccess/stylesheets//design/siteaccess/stylesheets/fonts/font.woff2)

The commit fix this bug.

[andrerom]

+0,5 as we don't have any unit tests here so a full +1 will need a bit more testing from community (one alternative is that we merge and await backports until the patch has been in circulation for some months to await possible feedback)