Null pointer exceptions caused by showTextureFiles on nonexistent directory from prefs

[ash2x3zb9cy]

VMTGen started crashing with NPEs upon opening. It ran fine a few times first. It seems the directory it's looking for textures in (which is stored in Preferences) no longer exists, and this possibility isn't being handled.
Issue was worked around by deleting the prefs using regedit.

$javaw.exe -jar ./VMTGen-1.2-BETA-rc1.jar
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
        at com.xyphos.vmtgen.GUI.showTextureFiles(GUI.java:2144)
        at com.xyphos.vmtgen.GUI.<init>(GUI.java:131)
        at com.xyphos.vmtgen.GUI$37.run(GUI.java:1824)
        at java.awt.event.InvocationEvent.dispatch(Unknown Source)
        at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
        at java.awt.EventQueue.access$500(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.awt.EventQueue$3.run(Unknown Source)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
        at java.awt.EventQueue.dispatchEvent(Unknown Source)
        at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
        at java.awt.EventDispatchThread.run(Unknown Source)