When opening a file from a chooser, don't return null

[hinerm]

Right now if you open a file with a file chooser, e.g. via File > Open, if SCIFIO can't open it we return null. However, this causes the typical File > Open code to execute, which causes the IJ1 open file dialog to pop with no explanation that SCIFIO couldn't support the format.

So if we intercept a File > Open call and SCIFIO fails but selected a file, we need to continue in IJ1 with that selected file.