LUTFinder: defensive programming

Under certain circumstances, FileUtils.listContents() returns a
list with items whose getURI().getPath() returns null, such as
jar:file:/path/to/ij-data.jar!/luts/.

Simply do not give up so easily, but accept all kinds of weird input
-- this is in line with Postel's law that one should follow always,
anyway.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
TextDisplayPanel: make clicking on links work

You also see the URL of a link in ImageJ's status bar, when hovering the
mouse... we can all throw our browsers away now and just use ImageJ!