EM_COINC Circular called before ext trigger added

See Sentry Error: https://sentry.io/organizations/ligo-caltech/issues/991640570/?environment=playground&environment=production&project=1425216&query=is%3Aunresolved&statsPeriod=7d

This error occurred because that are no external triggers yet associated to the superevent. External events are added after a RAVEN search is performed, where the 'EM_COINC' label is applied, and this label triggers the EM_COINC circular to be generated. However the circular is finishing before the external event is added.