openib btl unsafe in case of extremely low srq settings

diff -r eb32fad15d19 ompi/mca/btl/openib/btl_openib_component.c
--- a/ompi/mca/btl/openib/btl_openib_component.c	Wed Jun 09 17:39:55 2010 +0200
+++ b/ompi/mca/btl/openib/btl_openib_component.c	Fri Jun 18 17:00:12 2010 +0200
@@ -3543,6 +3543,11 @@ int mca_btl_openib_post_srr(mca_btl_open
     }
     num_post = rd_curr_num - openib_btl->qps[qp].u.srq_qp.rd_posted;
 
+    if (0 == num_post) {
+        OPAL_THREAD_UNLOCK(&openib_btl->ib_lock);
+        return OMPI_SUCCESS;
+    }
+
     for(i = 0; i < num_post; i++) {
         ompi_free_list_item_t* item;
         OMPI_FREE_LIST_WAIT(&openib_btl->device->qps[qp].recv_free, item, rc);