Replace more direct accessors to ItemDictionary

SabreTools.DatTools/Cleaner.cs

@@ -169,9 +169,6 @@ namespace SabreTools.DatTools
                     // Run cleaning per item
                     CleanDatItem(item);
                 }
-
-                // Assign back for caution
-                datFile.Items[key] = items;
             }
         }
 

SabreTools.DatTools/Splitter.cs

@@ -838,7 +838,7 @@ namespace SabreTools.DatTools
                 }
 
                 // Add the current machine to the current DatFile
-                currentDat.Items[machine] = items;
+                currentDat.Add(machine, items);
                 currentSize += machineSize;
             }
 

SabreTools.DatTools/Verification.cs

@@ -229,9 +229,6 @@ namespace SabreTools.DatTools
                     if (items[i].GetFieldValue<Source?>(DatItem.SourceKey)?.Index != int.MaxValue)
                         items[i].SetFieldValue<bool?>(DatItem.RemoveKey, true);
                 }
-
-                // Set the list back, just in case
-                datFile.Items[key] = items;
             }
 
             watch.Stop();