SLR: Ensure that uncompressed size is plausible
If we cannot detect the uncompressed size, then it's reported as 0. This results in the blocking factor being 1, which makes tar extremely slow.
Set the size to 250 MB, a rough upper bound on the runtime archives we expect to be dealing with. This way the zenity progress bar may stop a little short.
Edited by Timothee Besset