Fix memory leak `sval` when out of memory in `Data_Wrap_Struct()`

include/mruby/data.h

@@ -39,10 +39,11 @@ MRB_API struct RData *mrb_data_object_alloc(mrb_state *mrb, struct RClass* klass
 #define Data_Wrap_Struct(mrb,klass,type,ptr)\
   mrb_data_object_alloc(mrb,klass,ptr,type)
 
-#define Data_Make_Struct(mrb,klass,strct,type,sval,data) do { \
+#define Data_Make_Struct(mrb,klass,strct,type,sval,data_obj) do { \
+  (data_obj) = Data_Wrap_Struct(mrb,klass,type,NULL);\
   (sval) = mrb_malloc(mrb, sizeof(strct));                     \
   { static const strct zero = { 0 }; *(sval) = zero; };\
-  (data) = Data_Wrap_Struct(mrb,klass,type,sval);\
+  (data_obj)->data = (sval);\
 } while (0)
 
 #define RDATA(obj)         ((struct RData *)(mrb_ptr(obj)))