Fix sync service

[fbac]

The sync service broke because of a subtle bug introduced in the renewed SelectGatewayEnvelopeByOriginators.

With more than one originator ID it can happen that:

• service tries to subscribe to 100, 200, 300
• the limit imposed per originator is max_envelopes/num_originators
• the condition if receivedEnvs < maxEnv { break } is hit.