* enc/utf_32be.c (utf32be_mbc_enc_len): check arguments precisely.
  [ruby-core:79966] [Bug #13292]

* enc/utf_32le.c (utf32le_mbc_enc_len): ditto.

* regenc.h (UNICODE_VALID_CODEPOINT_P): predicate for valid
  Unicode codepoints.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57816 b2dd03c8-39d4-4d8f-98ff-823fe69b080e