Don't drop the last character of Image Description, or ascii in general

I'm finding that some exif strings are NULL terminated and some
aren't.  Avoid the "TODO: but I'm not sure why", by always reading the
value length characters and then removing from the first NULL or any
terminating spaces.  I see the "motion" webcam motion detection
program will NULL terminate dates, but not Image Description, and
previously "iNumValues - 1" would truncate the last character.
keep all the printable characters in ascii

This way just the non-printable ones are discarded.