emotty: fix for undefined $TTY (FreeBSD) (#7844)

See https://github.com/robbyrussell/oh-my-zsh/pull/6731#issuecomment-449653115

plugins/emotty/emotty.plugin.zsh

@@ -25,8 +25,14 @@ emotty_default_set=emoji
 function emotty() {
   # Use emotty set defined by user, fallback to default
   local emotty=${_emotty_sets[${emotty_set:-$emotty_default_set}]}
-  # Parse $TTY number, normalizing it to an emotty set index
-  (( tty = (${TTY##/dev/tty} % ${#${=emotty}}) + 1 ))
+
+  # Parse tty number via prompt expansion. %l equals:
+  # - N      if tty = /dev/ttyN
+  # - pts/N  if tty = /dev/pts/N
+  local tty = ${${(%):-%l}##pts/}
+  # Normalize it to an emotty set index
+  (( tty = (tty % ${#${=emotty}}) + 1 ))
+
   local character_name=${${=emotty}[tty]}
   echo "${emoji[${character_name}]}${emoji2[emoji_style]}"
 }