Errorhandler: don't fallback to COMM_WORLD, pass NULL instead

MPI 4.0, page 27 says

> some errors may not have a communicator, window, or file on which
> an error may be raised. In such cases,
> these errors will be raised on the communicator MPI_COMM_SELF when
> using the World Model (see Section 11.2) [...]

By passing NULL (instead of MPI_COMM_WORLD), to ompi_errhandler_invoke
we trigger the right selection of the object to invoke the error on.

Signed-off-by: Joseph Schuchart <schuchart@icl.utk.edu>

Author: devreal

ompi/errhandler/errhandler_invoke.c

@@ -200,9 +200,9 @@ int ompi_errhandler_request_invoke(int count,
         break;
     default:
         /* Covers REQUEST_GEN, REQUEST_NULL, REQUEST_MAX */
-        return ompi_errhandler_invoke(MPI_COMM_WORLD->error_handler,
-                                      MPI_COMM_WORLD,
-                                      MPI_COMM_WORLD->errhandler_type,
+        return ompi_errhandler_invoke(NULL,
+                                      NULL,
+                                      0,
                                       ec, message);
         break;
     }