Assert that there's no outstanding current state that needs to be flushed from the vbo in _mesa_load_state_parameters().

Several of the state parameters use current state (such as materials).
Need to make sure those values are not stale.

src/mesa/shader/prog_statevars.c

@@ -815,6 +815,8 @@ _mesa_load_state_parameters(GLcontext *ctx,
    if (!paramList)
       return;
 
+   assert(ctx->Driver.NeedFlush == 0);
+
    for (i = 0; i < paramList->NumParameters; i++) {
       if (paramList->Parameters[i].Type == PROGRAM_STATE_VAR) {
          _mesa_fetch_state(ctx,