Launcher: ensure cache rebuild dialog stays open.

Disable the auto-close behaviour, which was causing us to end the
rebuild too early, and then corrupt the DB

src/GUI/QtLauncher.cxx

@@ -107,6 +107,8 @@ void initNavCache()
                                            | Qt::MSWindowsFixedSizeDialogHint);
         rebuildProgress.setWindowModality(Qt::WindowModal);
         rebuildProgress.setMinimumWidth(600);
+        rebuildProgress.setAutoReset(true);
+        rebuildProgress.setAutoClose(false);
         rebuildProgress.show();
     
         QTimer updateTimer;