Use length property instead of size() member function

size() function is not recommended in jQuery, use length property.
It maybe make trouble in gantt-progress-line.

---------------------- public/javascripts/application.js ----------------------
index b05e28d..cf33f12 100644
@@ -659,12 +659,12 @@ function beforeShowDatePicker(input, inst) {
   var default_date = null;
   switch ($(input).attr("id")) {
     case "issue_start_date" :
- if ($("#issue_due_date").size() > 0) {
+ if ($("#issue_due_date").length > 0) {
         default_date = $("#issue_due_date").val();
       }
       break;
     case "issue_due_date" :
- if ($("#issue_start_date").size() > 0) {
+ if ($("#issue_start_date").length > 0) {
         var start_date = $("#issue_start_date").val();
         if (start_date != "") {
           start_date = new Date(Date.parse(start_date));

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: redmine 4.0.6-2
ProcVersionSignature: Ubuntu 5.4.0-31.35-generic 5.4.34
Uname: Linux 5.4.0-31-generic x86_64
ApportVersion: 2.20.11-0ubuntu27
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Tue May 19 22:37:21 2020
InstallationDate: Installed on 2018-05-04 (745 days ago)
InstallationMedia: Ubuntu 17.10 "Artful Aardvark" - Release amd64(20180108.1)
PackageArchitecture: all
SourcePackage: redmine
UpgradeStatus: Upgraded to focal on 2020-05-10 (9 days ago)