nlecomposition: Suppress error from child during sync state with parent

nlecomposition: Suppress error from child during sync state with parent

This commit is to ensure cleanup internal elements on state change failure.

nlecomposition posts its own error message after cleanup child.
If we don't suppress child error, meanwhile, an application
triggered downward state change (resulting from child error message)
might be able to reach nlecomposition before internal cleaning child up.
That eventually results to downward state change failure.