topo/base: correctly support MPI_UNWEIGHTED in mca_topo_base_dist_graph_neighbors()

Thanks Jun Kudo for the bug report.

(cherry picked from commit open-mpi/ompi@8aff67c)

Author: ggouaillardet

ompi/mca/topo/base/topo_base_dist_graph_neighbors.c

@@ -8,7 +8,7 @@
  *                         reserved.
  * Copyright (c) 2011-2013 Inria.  All rights reserved.
  * Copyright (c) 2011-2013 Universite Bordeaux 1
- * Copyright (c) 2014-2015 Research Organization for Information Science
+ * Copyright (c) 2014-2016 Research Organization for Information Science
  *                         and Technology (RIST). All rights reserved.
  */
 
@@ -40,13 +40,13 @@ int mca_topo_base_dist_graph_neighbors(ompi_communicator_t *comm,
 
     for (i = 0; i < maxindegree; ++i) {
         sources[i] = dg->in[i];
-        if (NULL != dg->inw) {
+        if (MPI_UNWEIGHTED != sourceweights && NULL != dg->inw) {
             sourceweights[i] = dg->inw[i];
         }
     }
     for (i = 0; i < maxoutdegree; ++i) {
         destinations[i] = dg->out[i];
-        if (NULL != dg->outw) {
+        if (MPI_UNWEIGHTED != destweights && NULL != dg->outw) {
             destweights[i] = dg->outw[i];
         }
     }