Fix off-by-one error of argc

Fix ruby/ruby#9562

ruby.c

@@ -1369,14 +1369,14 @@ proc_long_options(ruby_cmdline_options_t *opt, const char *s, long argc, char **
     (((allow_envopt) || !envopt) ? (void)0 :                            \
      rb_raise(rb_eRuntimeError, "invalid switch in RUBYOPT: --" name))
 # define need_argument(name, s, needs_arg, next_arg)                    \
-    ((*(s) ? !*++(s) : (next_arg) && (!argc || !((s) = argv[1]) || (--argc, ++argv, 0))) && (needs_arg) ? \
+    ((*(s) ? !*++(s) : (next_arg) && (argc <= 1 || !((s) = argv[1]) || (--argc, ++argv, 0))) && (needs_arg) ? \
      rb_raise(rb_eRuntimeError, "missing argument for --" name)         \
      : (void)0)
 # define is_option_with_arg(name, allow_hyphen, allow_envopt)           \
     is_option_with_optarg(name, allow_hyphen, allow_envopt, Qtrue, Qtrue)
 # define is_option_with_optarg(name, allow_hyphen, allow_envopt, needs_arg, next_arg) \
     (strncmp((name), s, n = sizeof(name) - 1) == 0 && is_option_end(s[n], (allow_hyphen)) && \
-     (s[n] != '-' || s[n+1]) ?                                          \
+     (s[n] != '-' || (s[n] && s[n+1])) ?                                \
      (check_envopt(name, (allow_envopt)), s += n,                       \
       need_argument(name, s, needs_arg, next_arg), 1) : 0)
 

test/ruby/test_rubyoptions.rb

@@ -541,6 +541,16 @@ class TestRubyOptions < Test::Unit::TestCase
                       /invalid name for global variable - -# \(NameError\)/)
   end
 
+  def test_option_missing_argument
+    assert_in_out_err(%w(-0 --enable), "", [], /missing argument for --enable/)
+    assert_in_out_err(%w(-0 --disable), "", [], /missing argument for --disable/)
+    assert_in_out_err(%w(-0 --dump), "", [], /missing argument for --dump/)
+    assert_in_out_err(%w(-0 --encoding), "", [], /missing argument for --encoding/)
+    assert_in_out_err(%w(-0 --external-encoding), "", [], /missing argument for --external-encoding/)
+    assert_in_out_err(%w(-0 --internal-encoding), "", [], /missing argument for --internal-encoding/)
+    assert_in_out_err(%w(-0 --backtrace-limit), "", [], /missing argument for --backtrace-limit/)
+  end
+
   def test_assignment_in_conditional
     Tempfile.create(["test_ruby_test_rubyoption", ".rb"]) {|t|
       t.puts "if a = 1"