DiskProbe: fix crash when trying to edit a package directory

/system and /home/config would crash diskprobe because DataEditor would
be left in an incompletely initialized state.

Also fix a memory leak: fAttribute was never freed, but is allocated with
strdup.

Fixes #10428.
DiskProbe: don't set a maximal size for the data view

We want the view to expand and fill the horizontal space as much as
possible.