Fix a potentially serious bug discovered by BEAM.


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13666 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/auxprogs/valgrind-di-server.c b/auxprogs/valgrind-di-server.c
index f7a0ba0..2889d26 100644
--- a/auxprogs/valgrind-di-server.c
+++ b/auxprogs/valgrind-di-server.c
@@ -780,7 +780,7 @@
          this slot.  But check anyway. */
       Bool ok = True;
       if (req_session_id != conn_state[conn_no].session_id) {
-         req = mk_Frame_asciiz("FAIL", "READ: invalid session ID");
+         res = mk_Frame_asciiz("FAIL", "READ: invalid session ID");
          ok = False;
       }
       /* Check we're connected to a file, and if so range-check the