LDAP resolver: Improve error message when invalid UUID is passed
LDAP resolver: Improve error message when invalid UUID is passed

If the UUID contains non-ASCII characters, it is invalid.  However,
without this fix, parsing the UUID fails with a generic
UnicodeDecodeError.

Working on #754

privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea,privacyidea/privacyidea