Qt: Fix accordion frame height calculation.

Change-Id: I32d2ea2ff34544e285b52e4e35e035306c33d3aa
Reviewed-on: https://code.wireshark.org/review/5935
Reviewed-by: Gerald Combs <gerald@wireshark.org>
Qt: Don't clear the capture file properties.

Don't clear the contents of the capture file properties dialog when the
capture closes. Retaining the contents lets users compare the properties
for multiple files.

Change-Id: I6bf684e7bd996f22032ec3d0adcddc343bb17992
Reviewed-on: https://code.wireshark.org/review/5937
Reviewed-by: Gerald Combs <gerald@wireshark.org>