Facter burns to the floor if there are invalid cahracters in dmidecode

One server has some invalid (looks like binary data/corruption) in the DMI-data. Productname and -manufacturer are garbled. On one hand this should not happen, on the other hand puppet(facter) should not break over it.
This change should just replace the invalid characters with a questionmark-gliph-thingy, and continue not burning down.

https://github.com/puppetlabs/facter/pull/2448