JFileChooser: NPE when creating read-only file chooser

JFileChooser now supports a UI defaults property "FileChooser.readOnly" which
prevents creation of new folders and renaming files. If setting this property
to false, then FilePane crashes with a NullPointerException.

java.lang.NullPointerException
        at sun.swing.FilePane.addActionsToMap(FilePane.java:354)
        at sun.swing.FilePane.createActionMap(FilePane.java:346)
        at sun.swing.FilePane.<init>(FilePane.java:124)
        at javax.swing.plaf.metal.MetalFileChooserUI.installComponents(MetalFile
ChooserUI.java:185)
        at javax.swing.plaf.basic.BasicFileChooserUI.installUI(BasicFileChooserU
I.java:135)
        [...]

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