Fix a bug introduced in r18725

ompi_info will crash due to a reference to a unalloced struct.  Add a check for
this struct to prevent this crash.

This commit was SVN r18727.

The following SVN revision numbers were found above:
  r18725 --> open-mpi/ompi@c2351d39f1

ompi/mca/btl/openib/btl_openib_iwarp.c

@@ -214,7 +214,7 @@ void mca_btl_openib_free_rdma_addr_list(void)
 {
     opal_list_item_t *item;
 
-    if (0 != opal_list_get_size(myaddrs)) {
+    if (NULL != myaddrs && 0 != opal_list_get_size(myaddrs)) {
         for (item = opal_list_get_first(myaddrs);
              item != opal_list_get_end(myaddrs);
              item = opal_list_get_next(item)) {
@@ -222,9 +222,8 @@ void mca_btl_openib_free_rdma_addr_list(void)
             opal_list_remove_item(myaddrs, item);
             OBJ_RELEASE(addr);
         }
+       OBJ_RELEASE(myaddrs);
     }
-
-    OBJ_RELEASE(myaddrs);
 }
 #else
 uint64_t mca_btl_openib_get_iwarp_subnet_id(struct ibv_device *ib_dev)