修复指令无法识别时可能导致的npe

app/src/main/java/com/bgycc/smartcanteen/activity/MainActivity.java

@@ -274,9 +274,14 @@ public class MainActivity extends AppCompatActivity implements View.OnClickListe
                 }
                 reset();
 
-                runningCommand = command;
                 runningRequest = commandViewModel.getCommandWorker(command);
+                if (runningRequest == null) {
+                    LogUtils.w(TAG, "该指令无法识别: " + command.toString());
+                    commandViewModel.commandFinish(command);
+                    return;
+                }
 
+                runningCommand = command;
                 workManager.beginUniqueWork(WORKER_NAME, ExistingWorkPolicy.REPLACE, runningRequest)
                         .enqueue();
                 runningLiveData = workManager.getWorkInfoByIdLiveData(runningRequest.getId());