Emojis using Zero Width Joiner show up as multiple emojis

As reported by urbec on IRC.

In xfce4-terminal 1.0.4 for example blackbird 🐦‍⬛ shows up as 🐦⬛ (Bird and Black Large Square) and Face with Spiral Eyes 😵‍💫 shows up as 😵💫 (Face with Crossed-Out Eyes and Dizzy) The font used is Noto Color Emoji. One example for a terminal emulator showing both properly is kitty 0.26.5