Do not destroy the transaction before it has returned

Destroy might be signaled before the dbus call has returned.

In destroy() we emit a `finished` event with code ExitUnknown, but
if the transaction returns an error we should have sent ExitFailed.

Furthermore, if we destroy the transaction object before
QDBusPendingCallWatcher fires, we might lose that event.

src/transactionprivate.cpp

@@ -188,14 +188,19 @@ void TransactionPrivate::runQueuedTransaction()
         return;
     }
 
-    if (reply.isFinished() && reply.isError()) {
-        q->errorCode(Transaction::ErrorInternalError, reply.error().message());
-        finished(Transaction::ExitFailed, 0);
+    if (reply.isFinished()) {
+        receivedReturn = true;
+        if (reply.isError()) {
+            receivedReturn = true;
+            q->errorCode(Transaction::ErrorInternalError, reply.error().message());
+            finished(Transaction::ExitFailed, 0);
+        }
         return;
     }
     auto watcher = new QDBusPendingCallWatcher(reply, q);
     q->connect(watcher, &QDBusPendingCallWatcher::finished,
                q, [this, q] (QDBusPendingCallWatcher *call) {
+        receivedReturn = true;
         QDBusPendingReply<> reply = *call;
         if (reply.isError()) {
             QDBusError error = reply.error();
@@ -204,6 +209,8 @@ void TransactionPrivate::runQueuedTransaction()
             q->errorCode(transactionError, error.message());
             finished(Transaction::ExitFailed, 0);
             destroy();
+        } else if (destroyOnReturn) {
+            destroy();
         }
         call->deleteLater();
     });
@@ -248,6 +255,12 @@ void TransactionPrivate::finished(uint exitCode, uint runtime)
 void TransactionPrivate::destroy()
 {
     Q_Q(Transaction);
+
+    if (!receivedReturn) {
+        destroyOnReturn = true;
+        return;
+    }
+
     if (p) {
        delete p;
        p = nullptr;

src/transactionprivate.h

@@ -82,6 +82,8 @@ class TransactionPrivate
     uint uid = 0;
     QString senderName;
     bool sentFinished = false;
+    bool receivedReturn = false;
+    bool destroyOnReturn = false;
     bool allowCancel = false;
     bool callerActive = false;