QtIFW

Fix initially deactivated buttons when selecting components to update

When entering component selection page for updates, force checking of
component model state change so we can enable or disable relevant
component selection buttons right when entering, not after first
selection change.

Task-number: QTIFW-1320
Change-Id: I86a94b70979f7064618186c539b0b7fc594d1481
Reviewed-by: Katja Marttila <katja.marttila@qt.io>