array.c (rb_ary_shift): small bug fix

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@11017 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

array.c

@@ -584,7 +584,7 @@ rb_ary_shift(VALUE ary)
     }
     else {
 	if (!FL_TEST(ary, ELTS_SHARED)) {
-	    RARRAY(ary)->ptr[0] = Qnil;
+	    RARRAY_PTR(ary)[0] = Qnil;
 	}
 	ary_make_shared(ary);
 	RARRAY(ary)->as.heap.ptr++;	/* shift ptr */