Bail out from password reset for invalid keys

[wet]

The key protecting the password reset event is ​a string of a known length of characters from a known character set.

Nevertheless, on the receiving end WordPress tries to ​filter out invalid characters from the key despite knowing that these must not be there in the first place.

I suggest to simply refuse working with invalid keys and handle that as an error condition.

[nacin]

wp_generate_password() is pluggable, and (as of 3.0) filterable. Best not to muck with this. It works fine as is.