Revert code.

lib.go

@@ -460,6 +460,7 @@ func readSheetFromFile(sc chan *indexedSheet, index int, rsheet xlsxSheet, fi *F
 		return
 	}
 	sheet := new(Sheet)
+	sheet.File = fi
 	sheet.Rows, sheet.Cols, sheet.MaxCol, sheet.MaxRow = readRowsFromSheet(worksheet, fi)
 	sheet.Hidden = rsheet.State == sheetStateHidden || rsheet.State == sheetStateVeryHidden
 	result.Sheet = sheet