Fix crash in QGC and report configuration errors to the configuring pilot.

For BOSS-899, https://github.com/mavlink/qgroundcontrol/issues/10035

- Fix crash in QGC:
    Application key wasn't set and so the AirMap shared state object
    hadn't been created.

- Report configuration errors to the configuring pilot:
    When attempting to load the flight list, the application key and
    pilot's username/password must be set.

src/Airmap/AirMapFlightPlanManager.cc

@@ -836,6 +836,19 @@ AirMapFlightPlanManager::loadFlightList(QDateTime startTime, QDateTime endTime)
 {
     //-- TODO: This is not checking if the state is Idle. Again, these need to
     //   queued up and handled by a worker thread.
+    if (!_shared.client()) {
+        // Pilot needs to set an AirMap API key to retrieve flight lists.
+        // The API key is associated with the application developer. It may be
+        // compiled-in with customized versions of QGC.
+        emit error(tr("Failed to get flight lists"), tr("AirMap application API key needed for flight lists."), tr("Set your AirMap application API key in Settings -> AirMap"));
+        return;
+    }
+    if (!_shared.isLoggedIn()) {
+        // Flights are associated with the pilot's AirMap account. Anonymous
+        // users have no flights and will have an empty flight list.
+        emit error(tr("Failed to get flight lists"), tr("AirMap username/password required for flight lists."), tr("Set your AirMap username/password in Settings -> AirMap"));
+        return;
+    }
     qCDebug(AirMapManagerLog) << "Preparing load flight list";
     _loadingFlightList = true;
     emit loadingFlightListChanged();

src/Airmap/AirMapSharedState.cc

@@ -44,6 +44,7 @@ AirMapSharedState::login()
     if (isLoggedIn() || _isLoginInProgress) {
         return;
     }
+    Q_ASSERT(nullptr != _client);
     _isLoginInProgress = true;
     if (_settings.userName == "") { //use anonymous login
         qCDebug(AirMapManagerLog) << "Anonymous authentication";