wta: Don't generate zero edges when we decided not to

This is currently only implemented for the case where --different-values is
supplied.

When the random experiment says that we should generate non-zero edge, we should
rule out the possibility that this edge gets assigned a random weight of zero.
With small --different-values, zero edges would have become way more likely.

src/random-wta/Generator.hs

@@ -32,9 +32,9 @@ genMonoidValue = asks ((monoid . spec) &&& differentValues) >>= \case
   (Powerset, Nothing) -> liftIO $ randomIO
   (Powerset, _) -> error $ "differentValues not supported for powerset" -- FIXME detect this early (and handle the case <=2)
   (OrWord, Nothing)   -> liftIO $ randomIO
-  (OrWord, Just x)   -> liftIO $ randomRIO (0, fromIntegral (x-1))
+  (OrWord, Just x)   -> liftIO $ randomRIO (1, fromIntegral x)
   (MaxInt, Nothing)   -> liftIO $ randomIO
-  (MaxInt, Just x)   -> liftIO $ randomRIO (0, x-1)
+  (MaxInt, Just x)   -> liftIO $ randomRIO (1, x)
 
 genStates :: Generator m (Vector m)
 genStates = do