Fix assertion failure in vvp wide functor.

If the functor output is read before any values have propagated to
the functor inputs, the internal storage won't have been initialised.

vvp/vvp_net.cc

@@ -3421,7 +3421,8 @@ unsigned vvp_wide_fun_core::port_count() const
 vvp_vector4_t& vvp_wide_fun_core::value(unsigned idx)
 {
       assert(idx < nports_);
-      assert(port_values_);
+      if (port_values_ == 0)
+	    port_values_ = new vvp_vector4_t [nports_];
       return port_values_[idx];
 }