Ensure that the counter for unique ids is only ever advanced once

This fixes JOSM-18601, if the analysis was correct.

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

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

@@ -36,7 +36,10 @@ public class BoundingBoxMapWithAIDownloader extends BoundingBoxDownloader {
 
     @Override
     protected DataSet parseDataSet(InputStream source, ProgressMonitor progressMonitor) throws IllegalDataException {
-        DataSet ds = OsmReaderCustom.parseDataSet(source, progressMonitor, true);
+        DataSet ds;
+        synchronized (BoundingBoxMapWithAIDownloader.class) {
+            ds = OsmReaderCustom.parseDataSet(source, progressMonitor, true);
+        }
         GetDataRunnable.addMapWithAISourceTag(ds, MapWithAIPreferenceHelper.getMapWithAIUrl().stream()
                 .filter(map -> map.getOrDefault("url", "no-url").equals(url))
                 .map(map -> map.getOrDefault("source", MapWithAIPlugin.NAME)).findFirst().orElse(MapWithAIPlugin.NAME));