Fix an error that made impossible to read negative values when reading a struct.
Fix an error that made impossible to read negative values when reading a struct.

Signed-off-by: Michele Cattafesta <3a7fde424b91cc639bbca1d59a0d12454384870a@mesta-automation.com>

mesta1/s7netplus,killnine/s7netplus,daGnutt/s7netplus,pietervp/s7netplus