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.

(cherry picked from commit ad83a135e5)

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];
 }