card_data: use default member initializer

card.h

@@ -23,18 +23,18 @@ class group;
 struct chain;
 
 struct card_data {
-	uint32 code;
-	uint32 alias;
-	uint64 setcode;
-	uint32 type;
-	uint32 level;
-	uint32 attribute;
-	uint32 race;
-	int32 attack;
-	int32 defense;
-	uint32 lscale;
-	uint32 rscale;
-	uint32 link_marker;
+	uint32 code{ 0 };
+	uint32 alias{ 0 };
+	uint64 setcode{ 0 };
+	uint32 type{ 0 };
+	uint32 level{ 0 };
+	uint32 attribute{ 0 };
+	uint32 race{ 0 };
+	int32 attack{ 0 };
+	int32 defense{ 0 };
+	uint32 lscale{ 0 };
+	uint32 rscale{ 0 };
+	uint32 link_marker{ 0 };
 
 	void clear();
 };