Merge pull request #6291 from mrhaandi/fix-artifact-nullptr

Fix artifact->artifactID.hasValue() nullptr

client/netlag/PackRollbackGeneratorVisitor.cpp

@@ -52,9 +52,11 @@ void PackRollbackGeneratorVisitor::visitRebalanceStacks(RebalanceStacks & pack)
 	const auto * srcArmy = dynamic_cast<const CArmedInstance *>(srcObject);
 	const auto * dstArmy = dynamic_cast<const CArmedInstance *>(dstObject);
 
+	const auto * artifact = srcArmy->getStack(pack.srcSlot).getSlot(ArtifactPosition::CREATURE_SLOT);
+
 	if (srcArmy->getStack(pack.srcSlot).getTotalExperience() != 0 ||
 	   dstArmy->getStack(pack.srcSlot).getTotalExperience() != 0 ||
-	   srcArmy->getStack(pack.srcSlot).getSlot(ArtifactPosition::CREATURE_SLOT)->artifactID.hasValue())
+	   (artifact && artifact->artifactID.hasValue()))
 	{
 		// TODO: rollback creature artifacts & stack experience
 		return;