Fix #123269: Shadow jittering when navigating

When navigating the viewport, the shadow jittering wasn't always
updated anymore. Regression introduced by e1ee3ed7df

Pull Request: https://projects.blender.org/blender/blender/pulls/123282

source/blender/draw/engines/eevee_next/eevee_instance.cc

@@ -89,6 +89,9 @@ void Instance::init(const int2 &output_res,
   if (is_painting()) {
     sampling.reset();
   }
+  if (is_navigating() && scene->eevee.flag & SCE_EEVEE_SHADOW_JITTERED_VIEWPORT) {
+    sampling.reset();
+  }
 
   update_eval_members();