[DatFile] Add error if game contains more than one of the same item

SabreTools.Helper/Dats/Partials/DatFile.Bucketing.cs

@@ -138,6 +138,13 @@ namespace SabreTools.Helper.Dats
 					{
 						sortable.Add(newkey, new List<DatItem>());
 					}
+
+					// Here, we want to see if there is a duplicate-named file already in the game
+					if (sortable[newkey].Where(i => i.Name == rom.Name).Count() > 0)
+					{
+						logger.Error("Duplicate named-file '" + rom.Name + "' detected in machine '" + newkey + "'");
+					}
+
 					sortable[newkey].Add(rom);
 				}
 			}