Guard against potential NullPointerException for QtActivityDelegate

agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: FATAL EXCEPTION: main
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: Process: org.qtproject.example.tst_qsignalspy, PID: 5377
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: java.lang.NullPointerException: Attempt to invoke virtual method 'void org.qtproject.qt.android.QtDisplayManager.setSystemUiVisibility(int)' on a null object reference
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at org.qtproject.qt.android.QtActivityBase.onRestoreInstanceState(QtActivityBase.java:285)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.Activity.performRestoreInstanceState(Activity.java:1787)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.Instrumentation.callActivityOnRestoreInstanceState(Instrumentation.java:1503)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3823)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:225)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:205)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:177)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:98)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2443)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.os.Handler.dispatchMessage(Handler.java:106)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.os.Looper.loopOnce(Looper.java:205)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.os.Looper.loop(Looper.java:294)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at android.app.ActivityThread.main(ActivityThread.java:8177)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at java.lang.reflect.Method.invoke(Native Method)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:552)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.314  5377  5377 E AndroidRuntime: 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:971)
agent:2024/10/04 23:58:22 build.go:404: 10-04 23:58:21.337  5377  5377 I Process : Sending signal. PID: 5377 SIG: 9