Fix loop condition in `mrb_sym_all_symbols`

mrbgems/mruby-symbol-ext/src/symbol.c

@@ -25,7 +25,7 @@ mrb_sym_all_symbols(mrb_state *mrb, mrb_value self)
   mrb_sym i, lim;
   mrb_value ary = mrb_ary_new_capa(mrb, mrb->symidx);
 
-  for (i=1; i<MRB_PRESYM_MAX; i++) {
+  for (i=1; i<=MRB_PRESYM_MAX; i++) {
     mrb_ary_push(mrb, ary, mrb_symbol_value(i));
   }
   for (i=1, lim=mrb->symidx+1; i<lim; i++) {