driver: Make the redrawhook codepath conditional upon the memo= feature.
driver: Make the redrawhook codepath conditional upon the memo= feature.

Fixes #579 (zsh-autosuggestions interoperability).
Fixes #735 (ditto).

See https://github.com/zsh-users/zsh-syntax-highlighting/issues/579#issuecomment-650126055
See https://github.com/zsh-users/zsh-autosuggestions/issues/529#issuecomment-650481227

P71/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,zsh-users/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,phy1729/zsh-syntax-highlighting,P71/zsh-syntax-highlighting