check existence of airline augroup before overwriting statusline

autoload/airline/extensions.vim

@@ -93,7 +93,7 @@ function! airline#extensions#load_theme()
 endfunction
 
 function! s:sync_active_winnr()
-  if winnr() != s:active_winnr
+  if exists('#airline') && winnr() != s:active_winnr
     if airline#exec_funcrefs(s:ext._cursormove_funcrefs, 1)
       return
     endif

autoload/airline/extensions/tagbar.vim

@@ -12,7 +12,7 @@ function! s:check_statusline()
   " sets it to BufEnter, so the ordering is off: airline sets the statusline
   " first, and then tagbar overwrites it, so this detects that and changes it
   " back to the airline statusline.
-  if match(&statusline, '^%!Tagbar') >= 0
+  if exists('#airline') && match(&statusline, '^%!Tagbar') >= 0
     call airline#update_statusline()
   endif
 endfunction