Setting the childMode property to ParallelStates will result in an
invalid state machine. This is never checked (worse, we explicitly
allow it and have a constructor to set it), but it results in
findLCCA failing, which then results in a failing assert or crash.
This fix in this patch is to handle this case separately. The proper
fix would be to remove completely the ability to set the childMode
on a QStateMachine, but that will have to wait until Qt6.
Fixes: QTBUG-49975
Change-Id: I43692309c4d438ee1a9bc55fa4f65f8bce8e0a59
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
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