QtIFW

Do not allow unstable component install

Unstable component was installed if component had unresolved dependency
and was fetched from category. Fixed so that unstable component which is
not already installed gets never selected in restoreCheckState().

Task-id: QTIFW-1265
Change-Id: I04176d095f6d79b2aabae73b490adc36706f597a
Reviewed-by: Jani Heikkinen <jani.heikkinen@qt.io>