[ruby/json] fix issue reading off the end of the ByteBuffer if ptr > 0

Fix: ruby/json#859

ruby/json@67ebabec75

Co-Authored-By: Jean Boussier <[email protected]>

Author: 2 people

test/json/json_encoding_test.rb

@@ -31,6 +31,12 @@ def test_generate
     assert_equal @generated, JSON.generate(@utf_16_data, ascii_only: true)
   end
 
+  def test_generate_shared_string
+    # Ref: https://github.com/ruby/json/issues/859
+    s = "01234567890"
+    assert_equal '"234567890"', JSON.dump(s[2..-1])
+  end
+
   def test_unicode
     assert_equal '""', ''.to_json
     assert_equal '"\\b"', "\b".to_json