bpo-46280: Fix tracemalloc_copy_domain() (pythonGH-30591)

Test if tracemalloc_copy_traces() failed to allocated memory in
tracemalloc_copy_domain().

Author: vstinner

Modules/_tracemalloc.c

@@ -1242,6 +1242,9 @@ tracemalloc_copy_domain(_Py_hashtable_t *domains,
     _Py_hashtable_t *traces = (_Py_hashtable_t *)value;
 
     _Py_hashtable_t *traces2 = tracemalloc_copy_traces(traces);
+    if (traces2 == NULL) {
+        return -1;
+    }
     if (_Py_hashtable_set(domains2, TO_PTR(domain), traces2) < 0) {
         _Py_hashtable_destroy(traces2);
         return -1;