coll/libnbc: fix MPI_Ialltoallv with MPI_IN_PLACE and without MPI param check

ompi/mca/coll/libnbc/nbc_ialltoallv.c

@@ -54,12 +54,6 @@ int ompi_coll_libnbc_ialltoallv(const void* sendbuf, const int *sendcounts, cons
   rank = ompi_comm_rank (comm);
   p = ompi_comm_size (comm);
 
-  res = ompi_datatype_type_extent (sendtype, &sndext);
-  if (MPI_SUCCESS != res) {
-    NBC_Error("MPI Error in ompi_datatype_type_extent() (%i)", res);
-    return res;
-  }
-
   res = ompi_datatype_type_extent (recvtype, &rcvext);
   if (MPI_SUCCESS != res) {
     NBC_Error("MPI Error in ompi_datatype_type_extent() (%i)", res);
@@ -87,7 +81,13 @@ int ompi_coll_libnbc_ialltoallv(const void* sendbuf, const int *sendcounts, cons
     }
     sendcounts = recvcounts;
     sdispls = rdispls;
-  } else if (sendcounts[rank] != 0) {
+  } else {
+    res = ompi_datatype_type_extent (sendtype, &sndext);
+    if (MPI_SUCCESS != res) {
+      NBC_Error("MPI Error in ompi_datatype_type_extent() (%i)", res);
+      return res;
+    }
+    if (sendcounts[rank] != 0) {
       rbuf = (char *) recvbuf + rdispls[rank] * rcvext;
       sbuf = (char *) sendbuf + sdispls[rank] * sndext;
       res = NBC_Copy (sbuf, sendcounts[rank], sendtype, rbuf, recvcounts[rank], recvtype, comm);
@@ -95,6 +95,7 @@ int ompi_coll_libnbc_ialltoallv(const void* sendbuf, const int *sendcounts, cons
         return res;
       }
     }
+  }
 
   schedule = OBJ_NEW(NBC_Schedule);
   if (OPAL_UNLIKELY(NULL == schedule)) {