Recalculating layout after redrawing the list of currently used Add-Ons

(port from SLE11 bnc#517919) (bnc#831825)

See https://github.com/yast/yast-add-on/commit/8adcd44a3080a6bd82cea7b4cb31957a689d931f#L1R1104
for the original SLE11 change

- 3.0.2
Merge pull request #7 from yast/bnc_831825

Recalculating layout after redrawing the list of currently used Add-Ons