neovim: Do not react on BufWinEnter for floating windows

closes #1930

plugin/airline.vim

@@ -51,6 +51,10 @@ function! s:on_window_changed(event)
   if pumvisible() && (!&previewwindow || g:airline_exclude_preview)
     return
   endif
+  " work around a neovim bug: do not trigger on floating windows
+  if exists("*nvim_win_get_config") && !empty(nvim_win_get_config(0).relative)
+    return
+  endif
   " Handle each window only once, since we might come here several times for
   " different autocommands.
   let l:key = [bufnr('%'), s:active_winnr, winnr('$'), tabpagenr(), &ft]