fix(form_1_2): guard null date/start_working before .Value to prevent 500

GetForm2Report ("ร1. แบบฟอร์มเสนอขอปรับเปลี่ยนชื่อตำแหน่ง") called
.Value on nullable DateTime fields unconditionally, crashing with
InvalidOperationException whenever a record's date or start_working
was null — exactly what happened for form_1_2_uid
377a46dc-7131-4b58-ac7e-c9b54900ac34 (date is null in production).
Mirrors the null-check pattern the sibling GetForm3Report already
uses for the same kind of field.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0153wBt23EjW125ZsADwWVAs

Controllers/RoFive.Controller.cs

@@ -4112,14 +4112,20 @@ namespace rmutr_report.Controllers
         [ApiExplorerSettings(GroupName = "reports")]
         public IActionResult GetForm2Report([FromRoute] string type,
             [FromBody] form_1_2 form1)
+        {
+            if (form1.date != null)
             {
                 form1.dates = form1.date.Value.ToString("dd MMMM yyyy", CultureInfo.CreateSpecificCulture("th-TH"));
+            }
+            if (form1.start_working != null)
+            {
                 form1.day_start_workings =
                     form1.start_working.Value.ToString("dd", CultureInfo.CreateSpecificCulture("th-TH"));
                 form1.month_start_workings =
                     form1.start_working.Value.ToString("MMMM", CultureInfo.CreateSpecificCulture("th-TH"));
                 form1.year_start_workings =
                     form1.start_working.Value.ToString("yyyy", CultureInfo.CreateSpecificCulture("th-TH"));
+            }
             var form_1 = new List<form_1_2>() { form1 };
 
             Report report = new Report();