Keep number format on string cell content Undo, tdf#103234 follow-up

Change-Id: I18c281211e6eeb4816da13972c360df85d577491

sc/inc/stringutil.hxx

@@ -46,6 +46,12 @@ struct SAL_WARN_UNUSED SC_DLLPUBLIC ScSetStringParam
          */
         SpecialNumberOnly,
 
+        /**
+         * Keep an existing number format, do not set Text number format and do
+         * not set another number format.
+         */
+        Keep,
+
         /**
          * Never set Text number format.
          */

sc/source/ui/undo/undocell.cxx

@@ -457,6 +457,8 @@ void ScUndoSetCell::SetValue( const ScCellValue& rVal )
         {
             ScSetStringParam aParam;
             aParam.setTextInput();
+            // Undo only cell content, without setting any number format.
+            aParam.meSetTextNumFormat = ScSetStringParam::Keep;
             rDoc.SetString(maPos, rVal.mpString->getString(), &aParam);
         }
         break;