* encoding.c (rb_enc_set_index, rb_enc_associate_index): validate argument encoding index. * include/ruby/encoding.h (ENCODING_SET): use rb_enc_set_index() instead of setting inlined bits directly. git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41739 b2dd03c8-39d4-4d8f-98ff-823fe69b080e