tdf#171999 fixes field editing

Editing fields with conditional/hidden text and (previous/next) page number
resets required sub type which invalidates the fields.
Came in with
commit 9257e94e5d
Author: Noel Grandin <noelgrandin@gmail.com>
Date:   Sat Jul 5 16:35:17 2025 +0200

Change-Id: Ie07186be2fecad713dceb92f45e29621c99fe41e
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/204899
Tested-by: Jenkins
Reviewed-by: Oliver Specht <oliver.specht@cib.de>

sw/source/core/fields/fldbas.cxx

@@ -550,6 +550,8 @@ void SwField::SetUntypedSubType(sal_uInt16 n)
     case SwFieldIds::Database:
         static_cast<SwDBField*>(this)->SetSubType(static_cast<SwDBFieldSubType>(n));
         break;
+    case SwFieldIds::RefPageSet:
+        break;
     default:
         assert(n == 0 && "trying to set a subtype on something I don't know about");
         break;

sw/source/ui/fldui/flddok.cxx

@@ -610,6 +610,22 @@ bool SwFieldDokPage::FillItemSet(SfxItemSet* )
         case SwFieldTypesEnum::PageNumber:
         case SwFieldTypesEnum::GetRefPage:
         {
+            switch (nTypeId)
+            {
+                case SwFieldTypesEnum::NextPage:
+                    nSubType = static_cast<sal_uInt16>(SwPageNumSubType::Next);
+                    break;
+                case SwFieldTypesEnum::PreviousPage:
+                    nSubType = static_cast<sal_uInt16>(SwPageNumSubType::Previous);
+                    break;
+                case SwFieldTypesEnum::PageNumber:
+                    nSubType = static_cast<sal_uInt16>(SwPageNumSubType::Random);
+                    break;
+                default:
+                    break;
+            }
+
+
             if( SVX_NUM_CHAR_SPECIAL != nFormat &&
                 (SwFieldTypesEnum::PreviousPage == nTypeId || SwFieldTypesEnum::NextPage == nTypeId))
             {

sw/source/ui/fldui/fldfunc.cxx

@@ -549,6 +549,10 @@ bool SwFieldFuncPage::FillItemSet(SfxItemSet* )
         case SwFieldTypesEnum::ConditionalText:
             aVal = OUString::Concat(m_xCond1ED->get_text())
                    + OUStringChar(CONDITIONAL_FIELD_SEPARATOR) + m_xCond2ED->get_text();
+            nSubType = static_cast<sal_uInt16>(nTypeId);
+            break;
+        case SwFieldTypesEnum::HiddenText:
+            nSubType = static_cast<sal_uInt16>(nTypeId);
             break;
         case SwFieldTypesEnum::Dropdown :
         {