Make SPAC always default to "4" for the radar chooser.

Before this change,  AddeRadarChooser was using AddeImageChooser's default of
"1" which was apparently breaking the Hydro Class product.  After chatting
with Tommy and DaveS, it sounds like it is safe to default to "4" because
the server will still return smaller spacing (1 or 2 byte) if it is able.

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