Fix mapgen window reverting to flatland when selecting heightmap image

distribution/changelog.txt

@@ -14,6 +14,7 @@
 - Fix: [#23376] Peeps with balloons, hats and umbrellas may leave artifacts on screen.
 - Fix: [#23486] Object selection minimum requirements can be bypassed with close window hotkey.
 - Fix: [#23496] Newly spawned vehicles are invisible when spawned while the game is paused.
+- Fix: [#23509] Map generator window reverts to flatland after selecting a heightmap image.
 
 0.4.17 (2024-12-08)
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src/openrct2-ui/windows/MapGen.cpp

@@ -1546,6 +1546,7 @@ namespace OpenRCT2::Ui::Windows
                 // The window needs to be open while using the map
                 _heightmapLoaded = true;
                 _heightmapFilename = fs::u8path(path).filename().string();
+                _settings.algorithm = MapGenerator::Algorithm::heightmapImage;
                 SetPage(WINDOW_MAPGEN_PAGE_BASE);
             }
         }