MapillaryDownloader: If return is null, don't cache return

Signed-off-by: Taylor Smock <tsmock@meta.com>

Author: tsmock

src/main/java/org/openstreetmap/josm/plugins/mapillary/data/mapillary/MapillaryDownloader.java

@@ -63,6 +63,9 @@ public static Map<String, List<MapillaryNode>> downloadImages(final long... imag
             final JsonObject jsonObject = getUrlResponse(url);
             return jsonObject != null ? jsonObject.toString() : null;
         });
+        if (stringJson == null) {
+            metaDataCache.getICacheAccess().remove(url);
+        }
         final List<MapillaryNode> nodes;
         if (stringJson != null) {
             try (JsonReader jsonReader = Json