Fix bugs where the file picker windows disappear on @file mentions (#2442)

Co-authored-by: Arnon Keereena <arnon.keereena@accenture.com>

lua/avante/utils/init.lua

@@ -741,10 +741,12 @@ function M.throttle(func, delay)
 end
 
 function M.winline(winid)
-  local current_win = api.nvim_get_current_win()
-  api.nvim_set_current_win(winid)
-  local line = fn.winline()
-  api.nvim_set_current_win(current_win)
+  -- If the winid is not provided, then line number should be 1, so that it can land on the first line
+  if not vim.api.nvim_win_is_valid(winid) then return 1 end
+
+  local line = 1
+  vim.api.nvim_win_call(winid, function() line = fn.winline() end)
+
   return line
 end