PocoSQLSensorHistoryDao: fix parsing of timestamp
PocoSQLSensorHistoryDao: fix parsing of timestamp

The method fetch() has never been properly tested. The method did not
convert the sensor data timestamp correctly back to the Poco::Timestamp.

Fixes: 2421a7d8b58c ("PocoSQLSensorHistoryDao: new class")
Signed-off-by: Jan Viktorin <3eab6ac54c005c4408f608556a6663b7f2abede7@fit.vutbr.cz>

BeeeOn/server,BeeeOn/server,BeeeOn/server,BeeeOn/server