<AWT Dev> Review a fix for List leak

[artem malinko]

Hello, AWT Team.

Please review a fix for the issue:
https://bugs.openjdk.java.net/browse/JDK-8040076
The fix is available at:
http://cr.openjdk.java.net/~mcherkas/artem/webrev.01/

When method "void AwtList::SetMultiSelect" is invoked it invokes "void 
AwtComponent::CreateHWnd" where m_peerObject initialized. But at this 
stage m_peerObject already initialized and already holds ref to java 
List object. So original m_peerObject is lost and ref to java List lost 
as well. In the fix I've added check whether m_peerObject is initialized 
or not.

Thank you.