mruby should accept "-" as stdin

tools/mruby/mruby.c

@@ -61,13 +61,15 @@ parse_args(mrb_state *mrb, int argc, char **argv, struct _args *args)
   memset(args, 0, sizeof(*args));
 
   if (argc == 1) return -2;
-
   for (argc--,argv++; argc > 0; argc--,argv++) {
     char *item;
     if (argv[0][0] != '-') break;
 
-    if (strlen(*argv) <= 1)
-      return -1;
+    if (strlen(*argv) <= 1) {
+      argc--; argv++;
+      args->rfp = stdin;
+      break;
+    }
 
     item = argv[0] + 1;
     switch (*item++) {
@@ -127,7 +129,6 @@ append_cmdline:
     }
   }
 
-
   if (args->rfp == NULL && args->cmdline == NULL) {
     if (*argv == NULL) args->rfp = stdin;
     else if ((args->rfp = fopen(*argv, args->mrbfile ? "rb" : "r")) == NULL) {