Clear error message when Install Script download unavailable

Re: Ticket #166">Ticket #166 (which seems to be resolved now), it looks like the error message when a script installation fails is not clear. It would be a nice improvement if this could say something more user friendly, such as "source download currently unavailable" or "failed to retrieve" (using the reported example).

From the reported error, it looks like Webmin tries to extract the source even though the zip file wasn't downloaded. Maybe it would help to do a simple file test to make sure it exists before running the unzip command.

Closed (fixed)