BUG: GH12290 where tz_convert used values of uninitialized arrays
closes #12290

aha!
 @kawochen : Also, you should put "Closes gh-12306" in your commit message so that the issue gets automatically closed once the PR is merged.
 the closes directive for the actual PR Is created at merge time
 updated according to @gfyoung's comment
 thanks @kawochen and @gfyoung 
