fix availableScreenRect for applets/containments
--when an applet or desktop containment is not in the current activity and requests ::availableScreenRect() value, Plasma::Corona decides to return -1 as a valid screenId. That behavior can lead to applets going under plasma panels that have set visibility to AlwaysVisible. Such panels should always been taken into account when calculating the available screen geometry.
Edited by Michail Vourlakos