Combo throws IAE if no item is selected

simple test is here

```java
@Test
public void comboTest(){
new ShellMenu("Window","Preferences").select();
new DefaultShell("Preferences");
new DefaultTreeItem("JBoss Tools","JBoss Maven Integration").select();
new PushButton("Configure Maven Repositories...").click();
new DefaultShell("Maven Repositories");
new PushButton(" Add Repository...").click();
new DefaultShell("Add Maven Repository");
new DefaultGroup("Profile");
new DefaultCombo("Profile ID:").setSelection(4);
}
```