fix: Ensure that pattern matching an animation only produces a wildcard

Previously, it was possible for example to take an expression `match (? : Maybe Animation) with {Nothing -> ? ; Just x -> ?}`, then, by raising `Animation`, create `match (? : Animation) with {Nothing -> ? ; Just -> ? ; _ -> ?}`. Now we ensure that those first two nonsensical branches are removed.

Signed-off-by: George Thomas <[email protected]>

primer/src/Primer/Typecheck.hs

@@ -756,7 +756,7 @@ check t = \case
                 PatPrim (PrimChar p) -> pure p
                 _ -> Nothing
             -- some primitives do not admit any sensible notion of pattern matching
-            | tc == tAnimation -> pure True
+            | tc == tAnimation -> pure $ null brs
             | otherwise -> throwError' $ InternalError $ "Unknown primitive type: " <> show tc
         brs' <-
           if consistentBranches