Fix regression in handling null outcomes when resizing strategic games.

Re-building the strategic game outcomes table was not correctly
handling the case of null outcomes since the migration
to using std::shared_ptr.

Fixes #571.  Also affected changes to strategies in `pygambit`; a test
was extended to check this case.

Author: tturocy

ChangeLog

@@ -1,5 +1,12 @@
 # Changelog
 
+## [16.4.1] - unreleased
+
+### Fixed
+- Fixed a regression in which null outcomes in strategic game tables were not handled correctly
+  when changing the number of strategies in the game (#571)
+
+
 ## [16.4.0] - 2025-09-05
 
 ### General

src/games/gametable.cc

@@ -407,8 +407,8 @@ GameStrategy GameTableRep::NewStrategy(const GamePlayer &p_player, const std::st
     throw MismatchException();
   }
   IncrementVersion();
-  p_player->m_strategies.push_back(
-      std::make_shared<GameStrategyRep>(p_player.get(), p_player->m_strategies.size(), p_label));
+  p_player->m_strategies.push_back(std::make_shared<GameStrategyRep>(
+      p_player.get(), p_player->m_strategies.size() + 1, p_label));
   RebuildTable();
   return p_player->m_strategies.back();
 }
@@ -495,7 +495,7 @@ void GameTableRep::RebuildTable()
       }
     }
 
-    if (newindex >= 0) {
+    if (newindex >= 0 && iter->GetOutcome() != nullptr) {
       newResults[newindex] = iter->GetOutcome().get();
     }
   }

tests/test_players.py

@@ -80,6 +80,10 @@ def test_strategic_game_add_strategy():
     game = gbt.Game.new_table([2, 2])
     game.add_strategy(game.players[0], "new strategy")
     assert len(game.players[0].strategies) == 3
+    # This second add also ensures that we are testing the case where there
+    # are null outcomes in the table
+    game.add_strategy(game.players[1], "new strategy")
+    assert len(game.players[1].strategies) == 3
 
 
 def test_extensive_game_add_strategy():