fix(tabpages): renaming bug on reopened tab (#877)

vim.fn.tabpagenr gets the tab number but api.nvim_tabpage_set_var
expects tab id, meaning the tab rename would fail if a tab was closed
and reopened. This change passes 0 into api.nvim_tabpage_set_var
which will use the current focused tab without needing to retrieve
the id.

lua/bufferline/tabpages.lua

@@ -35,9 +35,8 @@ local function render(tabpage, is_active, style, highlights)
 end
 
 function M.rename_tab(tabnr, name)
-  if tabnr == 0 then tabnr = vim.fn.tabpagenr() end
   if name == "" then name = tostring(tabnr) end
-  api.nvim_tabpage_set_var(tabnr, "name", name)
+  api.nvim_tabpage_set_var(0, "name", name)
   ui.refresh()
 end