do nothing if PENDING inputs are exist
do nothing if PENDING inputs are exist

Originally, zsh-syntax-highlighting called highlight functions at every inputs.
It's OK for user's keyboard inputs. But when long inputs come from clipboard,
it cause noticeable slowdown.

danielshahaf/zsh-syntax-highlighting-debian,arcan1s/zsh-syntax-highlighting,psprint/zsh-syntax-highlighting,joshuarubin/dotfiles,g5pw/zsh-syntax-highlighting,P71/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,psprint/zsh-syntax-highlighting,stuha/wbr-zsh,phy1729/zsh-syntax-highlighting,nlevchuk/zsh-syntax-highlighting,joshuarubin/dotfiles,P71/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting-debian,codedecay/zsh-syntax-highlighting,danielshahaf/zsh-syntax-highlighting,ryexley/zsh-syntax-highlighting,nakamuray/zsh-syntax-highlighting,m0vie/zsh-syntax-highlighting,joshuarubin/dotfiles,phy1729/zsh-syntax-highlighting,fly19890211/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,x-way/zsh-syntax-highlighting,jimmijj/zsh-syntax-highlighting,zsh-readable/zsh-readable,m0vie/zsh-syntax-highlighting,joshuarubin/dotfiles,zsh-users/zsh-syntax-highlighting