Fix a bug in the ob1 optimizations that can cause a segfault.

btl sendi functions currently can not handle the descriptor being NULL. The
send inline optimization was assuming (incorrectly) that NULL was ok.

cmr=v1.7.5:ticket=trac:4149

This commit was SVN r30364.

The following Trac tickets were found above:
  Ticket 4149 --> https://svn.open-mpi.org/trac/ompi/ticket/4149

ompi/mca/pml/ob1/pml_ob1_isend.c

@@ -62,6 +62,7 @@ static inline int mca_pml_ob1_send_inline (void *buf, size_t count,
                                            ompi_proc_t *dst_proc, mca_bml_base_endpoint_t* endpoint,
                                            ompi_communicator_t * comm)
 {
+    mca_btl_base_descriptor_t *des = NULL;
     mca_pml_ob1_match_hdr_t match;
     mca_bml_base_btl_t *bml_btl;
     OPAL_PTRDIFF_TYPE lb, extent;
@@ -86,8 +87,6 @@ static inline int mca_pml_ob1_send_inline (void *buf, size_t count,
         opal_convertor_copy_and_prepare_for_send (dst_proc->proc_convertor,
                                                   (const struct opal_datatype_t *) datatype,
 						  count, buf, 0, &convertor);
-
-        /* find out the packed size of the data */
         opal_convertor_get_packed_size (&convertor, &size);
     }
 
@@ -100,12 +99,16 @@ static inline int mca_pml_ob1_send_inline (void *buf, size_t count,
     /* try to send immediately */
     rc = mca_bml_base_sendi (bml_btl, &convertor, &match, OMPI_PML_OB1_MATCH_HDR_LEN,
                              size, MCA_BTL_NO_ORDER, MCA_BTL_DES_FLAGS_PRIORITY | MCA_BTL_DES_FLAGS_BTL_OWNERSHIP,
-                             MCA_PML_OB1_HDR_TYPE_MATCH, NULL);
+                             MCA_PML_OB1_HDR_TYPE_MATCH, &des);
     if (count > 0) {
         opal_convertor_cleanup (&convertor);
     }
 
     if (OPAL_UNLIKELY(OMPI_SUCCESS != rc)) {
+        if (des) {
+            mca_bml_base_free (bml_btl, des);
+        }
+
 	return rc;
     }