Guard against Gio's null-view detach event (recents-wipe SIGABRT)

Gio's GioView.onDestroyView sends ViewEvent{View: 0} as its detach
signal when the view is destroyed — i.e. the activity going away on a
recents-wipe. handleEvent passed that zero straight through to
InitPgp/registerFragment, whose GetObjectClass(null) aborts the process
(JNI DETECTED ERROR: java_object == null in call to GetObjectClass).

Guard on both sides: handleEvent ignores the View == 0 detach signal
(a re-attach arrives as a fresh event with a live view), InitPgp
returns early on a zero view so unfiltered callers are covered, and
registerFragment null-checks as defense in depth. Same fix as pad
(fdbffc9); verified there on a Pixel 9 Pro / Android 17 where the
recents swipe used to crash the app.

cmd/passgo-gui/impl_android.go

@@ -23,6 +23,15 @@ func init() {
 func handleEvent(e event.Event) {
 	switch e := e.(type) {
 	case app.ViewEvent:
+		// View == 0 is Gio's detach signal: GioView.onDestroyView sends
+		// ViewEvent{View: 0} when the view is destroyed (e.g. the activity
+		// going away on a recents-wipe). There is nothing to register for a
+		// detached view; passing the null ref on would abort in JNI
+		// (GetObjectClass on null). A re-attach arrives as a fresh event
+		// with a live view.
+		if e.View == 0 {
+			return
+		}
 		initPgp(e.View)
 	}
 }

impl_android.go

@@ -49,6 +49,12 @@ func Java_st_wow_git_passgo_PgpConnect_installComplete(env *C.JNIEnv, class C.jc
 
 func InitPgp(view uintptr) {
 	log.Printf("InitPgp()")
+	// view == 0 is Gio's detach signal (GioView.onDestroyView); nothing to
+	// register. Guard here as well so callers that forward the event
+	// unfiltered cannot drive registerFragment with a null ref (JNI abort).
+	if view == 0 {
+		return
+	}
 	jvm = app.JavaVM()
 	SetJVM(jvm) // why?
 	RunInJVM(func(env *JNIEnv) {

jni_android.c

@@ -7,6 +7,14 @@
 
 void
 registerFragment(JNIEnv *env, jobject view) {
+	if (view == NULL) {
+		// Detach signal (Gio sends ViewEvent{View: 0} when the view is
+		// destroyed, e.g. the activity going away on a recents-wipe).
+		// The Go side already filters these; this guard keeps the JNI
+		// calls safe if one ever slips through (GetObjectClass on null
+		// aborts the process).
+		return;
+	}
 	jclass cls = (*env)->GetObjectClass(env, view);
 	jmethodID mid = (*env)->GetMethodID(env, cls, "getContext", "()Landroid/content/Context;");
 	jobject ctx = (*env)->CallObjectMethod(env, view, mid);