return 0 when not a git repo

before, 128 was returned, which could display an error,
but out of a git repo this should exit silently
fixes #2226

lib/git.zsh

@@ -2,7 +2,7 @@
 function git_prompt_info() {
   if [[ "$(git config --get oh-my-zsh.hide-status)" != "1" ]]; then
     ref=$(command git symbolic-ref HEAD 2> /dev/null) || \
-    ref=$(command git rev-parse --short HEAD 2> /dev/null) || return
+    ref=$(command git rev-parse --short HEAD 2> /dev/null) || return 0
     echo "$ZSH_THEME_GIT_PROMPT_PREFIX${ref#refs/heads/}$(parse_git_dirty)$ZSH_THEME_GIT_PROMPT_SUFFIX"
   fi
 }