Fix UBSan issue (#1615)

Signed-off-by: Dmitri Mokhov <[email protected]>

include/oneapi/tbb/concurrent_hash_map.h

@@ -1,5 +1,5 @@
 /*
-    Copyright (c) 2005-2022 Intel Corporation
+    Copyright (c) 2005-2025 Intel Corporation
 
     Licensed under the Apache License, Version 2.0 (the "License");
     you may not use this file except in compliance with the License.
@@ -467,9 +467,13 @@ class hash_map_iterator {
     friend class concurrent_hash_map;
 
     hash_map_iterator( const Container &map, std::size_t index, const bucket *b, node_base *n ) :
-        my_map(&map), my_index(index), my_bucket(b), my_node(static_cast<node*>(n))
+        my_map(&map), my_index(index), my_bucket(b), my_node(nullptr)
     {
-        if( b && !map_base::is_valid(n) )
+        // Cannot directly initialize to n, because it could be an invalid node pointer (e.g., when
+        // setting a midpoint for a 1-element range). If it is, try one from a subsequent bucket.
+        if( map_base::is_valid(n) )
+            my_node = static_cast<node*>(n);
+        else if( b )
             advance_to_next_bucket();
     }