parse.y: numbered parameters should not appear on toplevel.

Toplevel includes the top of the method/class/module definitions.

mrbgems/mruby-compiler/core/parse.y

@@ -6422,6 +6422,7 @@ parser_yylex(parser_state *p)
             nvars = nvars->cdr;
           }
           nvar = intn(p->nvars->car);
+          if (nvar != -2) {     /* numbered parameters never appear on toplevel */
             if (nvar == -1) {
               yywarning(p, "numbered parameter used in inner block");
             }
@@ -6433,6 +6434,7 @@ parser_yylex(parser_state *p)
             return tNUMPARAM;
           }
         }
+      }
       /* fall through */
     default:
       if (toklast(p) == '!' || toklast(p) == '?') {