Make git use sha when branch name is missing.

lib/git.zsh

 # get the name of the branch we are on
 function git_prompt_info() {
-  ref=$(git symbolic-ref HEAD 2> /dev/null) || return
+  ref=$(git symbolic-ref HEAD 2> /dev/null) || \
+  ref=$(git rev-parse --short HEAD 2> /dev/null) || return
   echo "$ZSH_THEME_GIT_PROMPT_PREFIX${ref#refs/heads/}$(parse_git_dirty)$ZSH_THEME_GIT_PROMPT_SUFFIX"
 }
 

plugins/git/git.plugin.zsh

@@ -50,13 +50,14 @@ alias gsd='git svn dcommit'
 # Usage example: git pull origin $(current_branch)
 #
 function current_branch() {
-  ref=$(git symbolic-ref HEAD 2> /dev/null) || return
+  ref=$(git symbolic-ref HEAD 2> /dev/null) || \
+  ref=$(git rev-parse --short HEAD 2> /dev/null) || return
   echo ${ref#refs/heads/}
 }
 
 function current_repository() {
-
-  ref=$(git symbolic-ref HEAD 2> /dev/null) || return
+  ref=$(git symbolic-ref HEAD 2> /dev/null) || \
+  ref=$(git rev-parse --short HEAD 2> /dev/null) || return
   echo $(git remote -v | cut -d':' -f 2)
 }