vppinfra: keep AddressSanitizer happy

The vector size must be increased before setting the element so that
AddressSanitizer can keep track of the accessible memory.

Type: fix

Change-Id: I7b13ce98ff29d98e643f399ec1ecb4681d3cec92
Signed-off-by: Benoît Ganne <bganne@cisco.com>
diff --git a/src/vppinfra/pool.h b/src/vppinfra/pool.h
index ef81609..ea22af4 100644
--- a/src/vppinfra/pool.h
+++ b/src/vppinfra/pool.h
@@ -295,8 +295,9 @@
   /* Preallocated pool? */
   if (ph->max_elts)
     {
-      ph->free_indices[_vec_len (ph->free_indices)] = index;
-      vec_inc_len (ph->free_indices, 1);
+      u32 len = _vec_len (ph->free_indices);
+      vec_set_len (ph->free_indices, len + 1);
+      ph->free_indices[len] = index;
     }
   else
     vec_add1 (ph->free_indices, index);