game: fix solving "parity min" games with multi-colored edges

* spot/twaalgos/game.cc: If the original acceptance is "parity min",
use min_set(), not max_set(), to read edge priorities.
* tests/python/game.py: Add a test case.
* NEWS: Mention the bug.

spot/twaalgos/game.cc

@@ -357,7 +357,8 @@ namespace spot
         // Takes an edge and returns the "equivalent" max odd parity
         auto equiv_par = [max, odd, next_max_par, inv = 2*max-1](const auto& e)
           {
-            par_t e_par = e.acc.max_set() - 1; // -1 for empty
+            par_t e_par =
+              (max ? e.acc.max_set() : e.acc.min_set()) - 1; // -1 for empty
             // If "min" and empty -> set to n
             if (!max & (e_par == -1))
               e_par = next_max_par;