Initialize table even if cflag is 0; tr_find see whether
del is empty or not.
* string.c (tr_find): nodel can't be NULL; if NULL, it means
it is not specified.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@29148 b2dd03c8-39d4-4d8f-98ff-823fe69b080e