Exit only if the fbterm session closed correctly

This prevents the previous behavior that exitted the zsh session
even if fbterm didn't start correctly.

plugins/fbterm/fbterm.plugin.zsh

@@ -2,7 +2,6 @@
 
 if (( ${+commands[fbterm]} )); then
 	if [[ "$TTY" = /dev/tty* ]] ; then
-		fbterm
+		fbterm && exit
-		exit
 	fi
 fi