Deal with Creatures being deleted before a battle they're part of.

Signed-off-by: Deukhoofd <Deukhoofd@gmail.com>

tests/BattleTests/CreatureTests.cpp

@@ -1,5 +1,6 @@
 #ifdef TESTS_BUILD
 #include "../../extern/doctest.hpp"
+#include "../../src/Battling/Models/Battle.hpp"
 #include "../../src/Battling/Models/CreateCreature.hpp"
 #include "../TestLibrary/TestLibrary.hpp"
 
@@ -54,4 +55,16 @@ TEST_CASE("Override Creature talent") {
     delete creature;
 }
 
+TEST_CASE("Creature can be deleted before battle is deleted") {
+    // This should not happen during normal battle executions, but can happen for certain GC solutions. We should not
+    // segfault in this case, but deal with it properly.
+    auto library = TestLibrary::Get();
+    auto creature = CreateCreature(library, "testSpecies1"_cnc, 1).Create();
+    auto battle = new Battle(library, {});
+    auto side = battle->GetSides()[0];
+    side->SetCreature(creature, 0);
+    delete creature;
+    delete battle;
+}
+
 #endif