title: flutter doctor : idevice_id returned an error
body: <p>I hava a question.When I restart my computer , "flutter doctor" is OK. And I can run my app successfully. But Once I run my app, The command "flutter doctor" is wrong. And if I restart my computer,"flutter doctor" will be ok again. is anyone met the same question, how to solve it
  Exception: idevice_id returned an error:</p>
  
  <pre><code>#0      IMobileDevice.getInfoForDevice (package:flutter_tools/src/ios/mac.dart:122:9)
  #1      IOSDevice.getAttachedDevices (package:flutter_tools/src/ios/devices.dart:152:53)
  #2      IOSDevices.pollingGetDevices (package:flutter_tools/src/ios/devices.dart:112:57)
  #3      PollingDeviceDiscovery.devices (package:flutter_tools/src/device.dart:163:52)
  #4      DeviceManager.getAllConnectedDevices (package:flutter_tools/src/device.dart:91:46)
  #5      DeviceValidator.validate (package:flutter_tools/src/doctor.dart:607:54)
  #6      Doctor.startValidatorTasks (package:flutter_tools/src/doctor.dart:105:52)
  #7      Doctor.diagnose (package:flutter_tools/src/doctor.dart:162:41)
  #8      _AsyncAwaitCompleter.start (dart:async/runtime/libasync_patch.dart:49:6)
  #9      Doctor.diagnose (package:flutter_tools/src/doctor.dart:152:24)
  #10     DoctorCommand.runCommand (package:flutter_tools/src/commands/doctor.dart:29:39)
  #11     _AsyncAwaitCompleter.start (dart:async/runtime/libasync_patch.dart:49:6)
  #12     DoctorCommand.runCommand (package:flutter_tools/src/commands/doctor.dart:28:42)
  #13     FlutterCommand.verifyThenRunCommand (package:flutter_tools/src/runner/flutter_command.dart:372:18)
  #14     _asyncThenWrapperHelper.&lt;anonymous closure&gt; (dart:async/runtime/libasync_patch.dart:77:64)
  #15     _rootRunUnary (dart:async/zone.dart:1132:38)
  #16     _CustomZone.runUnary (dart:async/zone.dart:1029:19)
  #17     _FutureListener.handleValue (dart:async/future_impl.dart:129:18)
  #18     Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:642:45)
  #19     Future._propagateToListeners (dart:async/future_impl.dart:671:32)
  #20     Future._complete (dart:async/future_impl.dart:476:7)
  #21     _SyncCompleter.complete (dart:async/future_impl.dart:51:12)
  #22     _AsyncAwaitCompleter.complete.&lt;anonymous closure&gt; (dart:async/runtime/libasync_patch.dart:33:20)
  #23     _rootRun (dart:async/zone.dart:1124:13)
  #24     _CustomZone.run (dart:async/zone.dart:1021:19)
  #25     _CustomZone.bindCallback.&lt;anonymous closure&gt; (dart:async/zone.dart:947:23)
  #26     _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
  #27     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)
  #28     _runPendingImmediateCallback (dart:isolate/runtime/libisolate_patch.dart:115:13)
  #29     _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:172:5)"
  </code></pre>