Add condition to bypass saveVisit() for the existing visit.

1. Description

EmrEncounterServiceImpl.save(EncounterTransaction) saves over and over again unnecessarily visits that are already persisted in the first place.

2. Dev Notes

The following call should only happen for new visits that have not been persisted yet: https://github.com/openmrs/openmrs-module-emrapi/blob/5b319dc22b05c67c9a76aa3bb471737c5acf5308/api/src/main/java/org/openmrs/module/emrapi/encounter/EmrEncounterServiceImpl.java#L143