remove warning on NAN_BOXING

src/vm.c

@@ -72,16 +72,18 @@ The value below allows about 60000 recursive calls in the simplest case. */
 static inline void
 stack_clear(mrb_value *from, size_t count)
 {
+#ifndef MRB_NAN_BOXING
   const mrb_value mrb_value_zero = { { 0 } };
 
   while (count-- > 0) {
-#ifndef MRB_NAN_BOXING
     *from++ = mrb_value_zero;
+  }
 #else
+  while (count-- > 0) {
     SET_NIL_VALUE(*from);
     from++;
-#endif
   }
+#endif
 }
 
 static inline void