upToAll: for ZnCharacterReadStream

I have created another pull request with an implementation for #upToAll: for ZnCharacterReadStream:
https://github.com/pharo-project/pharo/pull/634

Here is the case: https://pharo.fogbugz.com/f/cases/20905

CI checks are in progress.

Does that make it the first contribution in 2018? ;-)

Let me know what you think.

Happy New Year
Bernhard