merge revision(s) f748b911c9157a0bb86f38280ddfba72a55049b6: [Backport #17729]

	Fix infinite loop at illegal sequence [Bug #17729]

	As mblen returns -1 on failure, skip the first byte and try the
	succeeding bytes in that case.

	Close https://github.com/ruby/ruby/pull/4281
	---
	 eval_intern.h                 | 11 ++++++++++-
	 test/ruby/test_rubyoptions.rb |  5 +++++
	 2 files changed, 15 insertions(+), 1 deletion(-)

1 files changed, 5 insertions, 0 deletions

diff --git a/test/ruby/test_rubyoptions.rb b/test/ruby/test_rubyoptions.rb
index b7831948f0..0d0f4b4d7e 100644
--- a/test/ruby/test_rubyoptions.rb
+++ b/test/ruby/test_rubyoptions.rb
@@ -1075,6 +1075,11 @@ class TestRubyOptions < Test::Unit::TestCase
     end
   end
 
+  def test_rubylib_invalid_encoding
+    env = {"RUBYLIB"=>"\xFF", "LOCALE"=>"en_US.UTF-8", "LC_ALL"=>"en_US.UTF-8"}
+    assert_ruby_status([env, "-e;"])
+  end
+
   def test_null_script
     skip "#{IO::NULL} is not a character device" unless File.chardev?(IO::NULL)
     assert_in_out_err([IO::NULL], success: true)