imagecache: fix mistake in imagecache address checking.

imagecache: fix mistake in imagecache address checking.

This will still may not work if the server is behind a proxy, as this
could lead to the wrong IP being detected.

For clients with HTSPv7 support they will only get the /imagecache/ID
part of the URL and will have to add the rest.

Note: there will be a number of clients that may report v7 support
but not be fully compliant due to the release schedules etc... users
in this position will not be able to use the image caching.