Crash on message recieved before ready

[remijn]

When a message is received before the coordinator is ready, shepherd crashes with this error

zigbee-shepherd:request RSP <-- SYS:osalNvRead, status: 0 +163ms
zigbee-shepherd:request REQ --> SAPI:readConfiguration +12ms
zigbee-shepherd:request RSP <-- SAPI:readConfiguration, status: 0 +23ms
/Users/nick/Programming/zigbee-shepherd/lib/components/af.js:530
targetEp = af.controller.getCoord().getEndpoint(msg.dstendpoint); // => find local ep
^

TypeError: Cannot read property 'getEndpoint' of null
at dispatchIncomingMsg (/Users/nick/Programming/zigbee-shepherd/lib/components/af.js:530:44)
at Controller.incomingMsgHandler (/Users/nick/Programming/zigbee-shepherd/lib/components/af.js:663:12)
at emitOne (events.js:77:13)
at Controller.emit (events.js:169:7)
at Object.bridge._areqEventBridge (/Users/nick/Programming/zigbee-shepherd/lib/components/event_bridge.js:15:16)
at CcZnp. (/Users/nick/Programming/zigbee-shepherd/lib/components/controller.js:98:16)
at emitOne (events.js:77:13)
at CcZnp.emit (events.js:169:7)
at CcZnp._mtIncomingDataHdlr (/Users/nick/Programming/zigbee-shepherd/node_modules/cc-znp/lib/ccznp.js:367:14)
at /Users/nick/Programming/zigbee-shepherd/node_modules/cc-znp/lib/ccznp.js:333:22
at nextTickCallbackWith0Args (node.js:489:9)
at process._tickCallback (node.js:418:13)