fix: apply the cell style always

Author: mlopezFC

src/main/java/com/flowingcode/vaadin/addons/gridexporter/ExcelInputStreamFactory.java

@@ -430,8 +430,8 @@ private void fillHeaderOrFooter(
                 sheet
                     .getRow(sheet.getActiveCell().getRow())
                     .createCell(sheet.getActiveCell().getColumn());
-            cell.setCellStyle(style);
           }
+          cell.setCellStyle(style);
           Object value =
               (isHeader
                   ? headerOrFooter.getLeft()