DRBD: fix exception in volume menu after creating a resource

java.lang.NullPointerException
null
lcmc.gui.resources.drbd.VolumeMenu$2.action(VolumeMenu.java:110)
lcmc.gui.ClusterBrowser$DRBDMenuItemCallback.mouseOver(ClusterBrowser.java:2705)
lcmc.gui.resources.Info$10$1.run(Info.java:720)