[mob][photos] Remove face IDs that aren't associated with any cluster from getting added to the 'Only them' filter results

mobile/lib/db/ml/db.dart

@@ -1053,4 +1053,17 @@ class MLDataDB {
 
     return <String>{for (final row in result) row[clusterIDColumn]};
   }
+
+  Future<Set<int>> getAllFileIDsOfFaceIDsNotInAnyCluster() async {
+    final db = await instance.asyncDB;
+    final result = await db.getAll(
+      '''
+        SELECT DISTINCT file_id
+        FROM faces
+        LEFT JOIN face_clusters ON faces.face_id = face_clusters.face_id
+        WHERE face_clusters.face_id IS NULL;
+    ''',
+    );
+    return <int>{for (final row in result) row[fileIDColumn]};
+  }
 }

mobile/lib/utils/hierarchical_search_util.dart

@@ -103,6 +103,11 @@ Future<List<EnteFile>> getFilteredFiles(
       final fileIDsToAvoid =
           await MLDataDB.instance.getFileIDsOfClusterIDs(clusterIDsToAvoid);
 
+      final filesOfFaceIDsNotInAnyCluster =
+          await MLDataDB.instance.getAllFileIDsOfFaceIDsNotInAnyCluster();
+
+      fileIDsToAvoid.addAll(filesOfFaceIDsNotInAnyCluster);
+
       final result =
           intersectionOfSelectedFaceFiltersFileIDs.difference(fileIDsToAvoid);
       filter.matchedUploadedIDs.addAll(result);