Allow the creation of strcutres with count zero. And try to have a more friendly behavior

(even if I don't agree with it) by setting the lb, ub, true_lb and true_ub to zero.

This commit was SVN r10205.

ompi/datatype/dt_create_struct.c

@@ -30,6 +30,7 @@ int32_t ompi_ddt_create_struct( int count, const int* pBlockLength, const long*
 
     if( 0 == count ) {
         *newType = ompi_ddt_create( disp );
+        ompi_ddt_add( *newType, &ompi_mpi_datatype_null, 0, 0, 0);
         return OMPI_SUCCESS;
     }
 

ompi/mpi/c/type_create_struct.c

@@ -45,9 +45,9 @@ int MPI_Type_create_struct(int count,
         if( count < 0 ) {
             return OMPI_ERRHANDLER_INVOKE(MPI_COMM_WORLD, MPI_ERR_COUNT,
                                           FUNC_NAME);
-        } else if(NULL == array_of_blocklengths ||
-                  NULL == array_of_displacements ||
-                  NULL == array_of_types) {
+        } else if( (count > 0) && (NULL == array_of_blocklengths ||
+                                   NULL == array_of_displacements ||
+                                   NULL == array_of_types) ) {
             return OMPI_ERRHANDLER_INVOKE(MPI_COMM_WORLD, MPI_ERR_ARG, FUNC_NAME);
         } else if (NULL == newtype) {
             return OMPI_ERRHANDLER_INVOKE(MPI_COMM_WORLD, MPI_ERR_TYPE, FUNC_NAME);