BaseGameArea sticks in memory after undocking

[Loomie]

Describe the bug
After looking in a heap dump of our Zircon application I found a no longer shown GameArea (and its references). The problem is that Cobalt is not used properly 😛 In BaseGameArea.init an onChange listener is registered. But it is never unregistered! So the EventBus of Cobalt holds that listener forever. That listener has a reference to the GameArea and therefore to our own code.

To Reproduce

screen.dock(viewWithGameArea)
screen.dock(otherView)

Do a garbage collection (GC) and create a heap dump.

Expected behavior
No instance of the no longer used View should linger in the memory.

Screenshots

Desktop (please complete the following information):

• Version org.hexworks.zircon:zircon.core-jvm:2020.2.0-RELEASE

Additional context
Add any other context about the problem here.

[Loomie]

Created PR #377 with a proposed fix.

[nanodeath]

init block in question: https://github.com/Hexworks/zircon/blob/master/zircon.core/src/commonMain/kotlin/org/hexworks/zircon/api/game/base/BaseGameArea.kt#L49-L51