Add listener for buttons to check if they're on the first or last page when pressing directional buttons

[iCodeHaven]

`
backButton.setListener(event -> {
PaginatedGUI menu = (PaginatedGUI) event.getClickedInventory().getHolder();
if(currentPage <= 0) {
event.getWhoClicked().sendMessage(ChatColor.translateAlternateColorCodes('&', "&8\u00bb &fThere are no more previous pages."));
return;
}
menu.previousPage();
event.getWhoClicked().closeInventory();
event.getWhoClicked().openInventory(getInventory());
});

nextButton.setListener(event -> {
PaginatedGUI menu = (PaginatedGUI) event.getClickedInventory().getHolder();
if(currentPage >= getMaxPage()) {
event.getWhoClicked().sendMessage(ChatColor.translateAlternateColorCodes('&', "&8\u00bb &fThere are no more extra pages."));
return;
}
menu.nextPage();
event.getWhoClicked().closeInventory();
event.getWhoClicked().openInventory(getInventory());
});`

You have no checks to see if they're pressing the buttons on the first or last page, I added some for myself

[masterdoctor]

Thank you

[masterdoctor]

Anyone interested customizing the pagination items and messages, please see: https://github.com/masterdoctor/SpigotPaginatedGUI/wiki/Customizing-the-pagination-items