Fix an issue where onPostDownload wasn't called for the layer

Signed-off-by: Taylor Smock <taylor.smock@kaart.com>

src/main/java/org/openstreetmap/josm/plugins/mapwithai/backend/MapWithAIDataUtils.java

@@ -344,6 +344,7 @@ public final class MapWithAIDataUtils {
                 } finally {
                     lock.unlock();
                 }
+                toDownload.stream().map(MapWithAIDataUtils::bboxToBounds).forEach(layer::onPostDownloadFromServer);
             });
         }
         return !toDownload.isEmpty();