bug: Empty delta on startup

[webmasterkai]

Sometimes on startup the plugin sends out a delta that looks like:
{ path: undefined, value: undefined, context: undefined, source: undefined, '$source': 'cloud:undefined', timestamp: undefined }
Unfortunately sk server can't handle deltas that look like that and it continues to restart and crash.

Places SK fails

• /opt/signalk-server/lib/deltacache.js:45:27 var parts = msg.context.split('.')
• @signalk/signalk-schema/dist/fullsignalk.js:86 var identity = contextPath.split('.')[1];