Import process crashes with to "bogus" json entry

Currently, when running bin/update_all or bin/update_representatives, the process crashes due to a "bogus" MEP json entry missing a Birth element.

This causes import_representatives to crash since this field is used without check, without completing the import process.

In this specific instance, the parltrack data entry which causes the failure concerns a MEP name Maurizio Enzo LUPI (funnily, it seems to also cause an issue on parltrack, see https://github.com/civicdataeu/parltrack/issues/28).