SwitchList gives no feedback if all (or many) cars have no location set.

[GoogleCodeExporter]

It's possible for a user to leave the location of all freight cars at "No 
Value", and be surprised when no cars show up in SwitchList.

We ought to do a better job of showing this - either warning when some or all 
cars are in "No Value" ("Note: didn't assign 3 cars without a location),  
automatically placing new cars in "Workbench" and banning "No Value", etc.

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Original issue reported on code.google.com by rwbowdi...@gmail.com on 26 Apr 2013 at 4:35