Keep the rebuild away from a window a thread is still writing to

deleteLater destroyed a window whose model boxes a daemon thread was
still reporting into: a running download died with a RuntimeError, the
.part stayed on disk and the UI said nothing. Dropping the reference is
how the ordinary close path lets a window go, and the closures a thread
holds keep the object alive until it is done, so the rebuild now does
the same. While the transcriber or either model box is working the
rebuild is skipped altogether; _built_language keeps the old language,
so the next quiet save asks for it by itself.

The new window is also placed and turned to the old tab before it is
shown, so it no longer comes up at the default size and jumps. And
tests/test_ui.py now says that a save with a changed language emits
language_changed, and one without does not.

dikte/app.py

@@ -1103,15 +1103,20 @@ class Dikte:
 
     def open_settings(self):
         if self.settings_window is None:
-            self.settings_window = SettingsWindow(self.conf, self.meetings)
-            self.settings_window.applied.connect(self._apply_settings)
-            self.settings_window.language_changed.connect(self._reopen_settings)
-            self.settings_window.update_found.connect(self._found_update)
-            self.settings_window.finished.connect(self._settings_closed)
+            self._make_settings()
         self.settings_window.show()
         self.settings_window.raise_()
         self.settings_window.activateWindow()
 
+    def _make_settings(self):
+        """Build the window without showing it, so a caller that knows where
+        it belongs can place it first."""
+        self.settings_window = SettingsWindow(self.conf, self.meetings)
+        self.settings_window.applied.connect(self._apply_settings)
+        self.settings_window.language_changed.connect(self._reopen_settings)
+        self.settings_window.update_found.connect(self._found_update)
+        self.settings_window.finished.connect(self._settings_closed)
+
     def _settings_closed(self, *_):
         # Don't drop the object while its own signal is still being delivered.
         QTimer.singleShot(0, lambda: setattr(self, "settings_window", None))
@@ -1135,11 +1140,19 @@ class Dikte:
         # would drop the reference to the new window a moment after it is made.
         old.finished.disconnect(self._settings_closed)
         old.close()
-        old.deleteLater()
+        # No deleteLater: a daemon thread of the old window's may still be
+        # running, and a closure holding self is what keeps the object alive
+        # until the thread is done. Dropping the reference is how the ordinary
+        # close path lets a window go, and it is enough here too.
         self.settings_window = None
-        self.open_settings()
-        self.settings_window.tabs.setCurrentIndex(tab)
+        self._make_settings()
+        # Placed and turned to the old tab before it is shown, so the new
+        # window does not come up at the default size and jump.
         self.settings_window.setGeometry(geometry)
+        self.settings_window.tabs.setCurrentIndex(tab)
+        self.settings_window.show()
+        self.settings_window.raise_()
+        self.settings_window.activateWindow()
 
     def _apply_local(self):
         """Pass the local settings on, and hold the models ready if asked to.