fix java.lang.NullPointerException

[seamlink-aalves]

Description

We had a lot of errors on Google Play Console with the following error:

Exception java.lang.RuntimeException:
  at android.app.ActivityThread.performResumeActivity (ActivityThread.java:5378)
  at android.app.ActivityThread.handleResumeActivity (ActivityThread.java:5444)
  at android.app.servertransaction.ResumeActivityItem.execute (ResumeActivityItem.java:54)
  at android.app.servertransaction.ActivityTransactionItem.execute (ActivityTransactionItem.java:45)
  at android.app.servertransaction.TransactionExecutor.executeLifecycleState (TransactionExecutor.java:176)
  at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:97)
  at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2574)
  at android.os.Handler.dispatchMessage (Handler.java:106)
  at android.os.Looper.loopOnce (Looper.java:226)
  at android.os.Looper.loop (Looper.java:313)
  at android.app.ActivityThread.main (ActivityThread.java:8757)
  at java.lang.reflect.Method.invoke
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:571)
  at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1067)
Caused by java.lang.RuntimeException:
  at android.app.ActivityThread.deliverResults (ActivityThread.java:5994)
  at android.app.ActivityThread.performResumeActivity (ActivityThread.java:5348)
Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'void org.apache.cordova.CallbackContext.sendPluginResult(org.apache.cordova.PluginResult)' on a null object reference
  at de.niklasmerz.cordova.biometric.Fingerprint.lambda$sendError$1 (Fingerprint.java)
  at android.app.Activity.runOnUiThread (Activity.java:7494)
  at de.niklasmerz.cordova.biometric.Fingerprint.sendError (Fingerprint.java:161)
  at de.niklasmerz.cordova.biometric.Fingerprint.sendError (Fingerprint.java:132)
  at de.niklasmerz.cordova.biometric.Fingerprint.onActivityResult (Fingerprint.java:115)
  at org.apache.cordova.CordovaInterfaceImpl.onActivityResult (CordovaInterfaceImpl.java:160)
  at org.apache.cordova.CordovaActivity.onActivityResult (CordovaActivity.java:375)
  at android.app.Activity.dispatchActivityResult (Activity.java:8951)
  at android.app.ActivityThread.deliverResults (ActivityThread.java:5987)

This seems to happen only on certain devices.

This PR checks if the activity still exists to send the result back to cordova.

How did you test your changes?

We deployed our app in beta and the errors no longer appear and have no negative impact for users.