fix: patient null error in healthcare_services_to_invoice

if show_title_field_in_link in Patient doc is checked

healthcare/public/js/sales_invoice.js

@@ -77,7 +77,7 @@ var get_healthcare_services_to_invoice = function(frm) {
  'patient': frm.doc.patient
  });
  dialog.fields_dict["patient"].df.onchange = () => {
- var patient = dialog.fields_dict.patient.input.value;
+ var patient = dialog.get_value("patient");
  if(patient && patient!=selected_patient){
  selected_patient = patient;
  var method = "healthcare.healthcare.utils.get_healthcare_services_to_invoice";