fix: Capture filename BEFORE closing dialog to prevent nil

The onCloseWidget callback was clearing browser._custom_filename
when the dialog closed. But the download callbacks were reading
the filename AFTER closing the dialog, so they got nil, which
caused DownloadManager to fall back to server filename.

Fix: Capture browser._custom_filename into a local variable BEFORE
calling UIManager:close() on the dialogs.

Author: greywolf1499

ui/dialogs/book_info_dialog.lua

@@ -153,13 +153,15 @@ local function showFormatSelectionDialog(browser, item, downloadable, add_to_que
 			{
 				text = text,
 				callback = function()
+					-- IMPORTANT: Capture filename BEFORE closing dialogs
+					-- because onCloseWidget clears browser._custom_filename
+					local filename = browser._custom_filename
+
 					UIManager:close(browser.format_dialog)
 					if parent_dialog then
 						UIManager:close(parent_dialog)
 					end
 
-					-- Get the current filename at download time (not dialog creation time)
-					local filename = browser._custom_filename
 					local local_path = DownloadManager.getLocalDownloadPath(
 						browser, filename, dl.filetype, dl.acquisition.href)
 
@@ -473,9 +475,11 @@ function BookInfoDialog.build(browser, item)
 			table.insert(action_row, {
 				text = Constants.ICONS.DOWNLOAD .. " " .. _("Download") .. " (" .. string.upper(dl.filetype) .. ")",
 				callback = function()
+					-- Capture filename BEFORE closing dialog
+					local filename = browser._custom_filename
 					UIManager:close(browser.book_info_dialog)
 					local local_path = DownloadManager.getLocalDownloadPath(
-						browser, browser._custom_filename, dl.filetype, dl.acquisition.href)
+						browser, filename, dl.filetype, dl.acquisition.href)
 					DownloadManager.checkDownloadFile(browser, local_path, dl.acquisition.href,
 						browser.root_catalog_username, browser.root_catalog_password,
 						browser.file_downloaded_callback)
@@ -496,9 +500,11 @@ function BookInfoDialog.build(browser, item)
 			table.insert(action_row, {
 				text = "+" .. " " .. _("Queue"),
 				callback = function()
+					-- Capture filename BEFORE closing dialog
+					local filename = browser._custom_filename
 					UIManager:close(browser.book_info_dialog)
 					local local_path = DownloadManager.getLocalDownloadPath(
-						browser, browser._custom_filename, dl.filetype, dl.acquisition.href)
+						browser, filename, dl.filetype, dl.acquisition.href)
 					DownloadManager.addToDownloadQueue(browser, {
 						file     = local_path,
 						url      = dl.acquisition.href,