GH-4299 Don't hard crash on when missing network

launcher/net/NetJob.cpp

@@ -98,6 +98,12 @@ void NetJob::partProgress(int index, qint64 bytesReceived, qint64 bytesTotal)
 
 void NetJob::executeTask()
 {
+    if(!m_network) {
+        qCritical() << "Attempted to start NetJob" << objectName() << "without the network set!";
+        emitFailed(tr("Internal error: NetJob '%1' has been started without a network pointer!").arg(objectName()));
+        return;
+    }
+
     // hack that delays early failures so they can be caught easier
     QMetaObject::invokeMethod(this, "startMoreParts", Qt::QueuedConnection);
 }

launcher/net/NetJob.h

@@ -67,15 +67,6 @@ public slots:
     virtual bool abort() override;
     virtual void start(shared_qobject_ptr<QNetworkAccessManager> network) {
         m_network = network;
-        start();
-    }
-
-protected slots:
-    void start() override {
-        if(!m_network) {
-            throw "Missing network while trying to start " + objectName();
-            return;
-        }
         Task::start();
     }