* transcode.c (str_transcode0): scrub in the given encoding when
	  the source encoding is given, not in the encoding of the
	  receiver.  [ruby-core:75732] [Bug #12431]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@55905 b2dd03c8-39d4-4d8f-98ff-823fe69b080e