Potential NPE in case of exception in LazyDatabaseSchemaWorkbenchAdapter in readDatabaseSchema

JBIDE-6396 fix open the problem:

java.lang.NullPointerException
at org.hibernate.eclipse.console.workbench.LazyDatabaseSchemaWorkbenchAdapter.getChildren(LazyDatabaseSchemaWorkbenchAdapter.java:67)
at org.hibernate.eclipse.console.workbench.BasicWorkbenchAdapter.fetchDeferredChildren(BasicWorkbenchAdapter.java:106)
at org.eclipse.ui.progress.DeferredTreeContentManager$1.run(DeferredTreeContentManager.java:235)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:54)