better disabled highlighting for inactive windows on FocusLost

This will make sure that the current window will be highlighted as
expected, even if there are no other windows and all highlighting groups
will be correctly re-created as 'inactive'

references #1807

autoload/airline/highlighter.vim

@@ -223,11 +223,6 @@ function! airline#highlighter#highlight(modes, ...)
   let mapped = map(a:modes, 'v:val == a:modes[0] ? v:val : a:modes[0]."_".v:val')
   let suffix = a:modes[0] == 'inactive' ? '_inactive' : ''
   for mode in mapped
-    if mode == 'inactive' && winnr('$') == 1
-      " there exist no inactive windows, don't need to create all those
-      " highlighting groups
-      continue
-    endif
     if exists('g:airline#themes#{g:airline_theme}#palette[mode]')
       let dict = g:airline#themes#{g:airline_theme}#palette[mode]
       for kvp in items(dict)