for empty sections, make test return true
for empty sections, make test return true

fixes #1231

dalguji/vim-airline,chrisbra/vim-airline,bling/vim-airline,tschundler/dotfiles,HarmtH/vim-airline,yzhou61/vim-airline,tschundler/dotfiles,tschundler/dotfiles,rchicoli/vim-airline,unphased/vim-airline