[zsh] Re-initialize zle when widgets finish

zle automatically calls zle-line-init when it starts to read a new line. Many
Zsh setups use this hook to set the terminal into application mode, since this
will then allow defining keybinds based on the $terminfo variable (the escape
codes in said variable are only valid in application mode).

However, fzf resets the terminal into raw mode, rendering $terminfo values
invalid once the widget has finished. Accordingly, keyboard bindings defined
via $terminfo won’t work anymore.

This fixes the issue by calling zle-line-init when widgets finish. Care is taken
to not call this widget when it is undefined.

Fixes #279

shell/key-bindings.zsh

@@ -25,6 +25,7 @@ fzf-file-widget() {
   LBUFFER="${LBUFFER}$(__fsel)"
   local ret=$?
   zle redisplay
+  typeset -f zle-line-init >/dev/null && zle zle-line-init
   return $ret
 }
 zle     -N   fzf-file-widget
@@ -38,6 +39,7 @@ fzf-cd-widget() {
   cd "${$(eval "$cmd | $(__fzfcmd) +m $FZF_ALT_C_OPTS"):-.}"
   local ret=$?
   zle reset-prompt
+  typeset -f zle-line-init >/dev/null && zle zle-line-init
   return $ret
 }
 zle     -N    fzf-cd-widget
@@ -56,6 +58,7 @@ fzf-history-widget() {
     fi
   fi
   zle redisplay
+  typeset -f zle-line-init >/dev/null && zle zle-line-init
   return $ret
 }
 zle     -N   fzf-history-widget