Have sample update hook not refuse deleting a branch through push.

source ref might be 0000...0000 to delete a branch through git-push,
'git <remote> push :<branch>'.  The update hook should not decline this.

Signed-off-by: Gerrit Pape <pape@smarden.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

templates/hooks--update

@@ -41,7 +41,12 @@ if [ -z "$projectdesc" -o "$projectdesc" = "Unnamed repository; edit this file t
 fi
 
 # --- Check types
-newrev_type=$(git-cat-file -t $newrev)
+# if $newrev is 0000...0000, it's a commit to delete a branch
+if [ -z "${newrev##0*}" ]; then
+	newrev_type=commit
+else
+	newrev_type=$(git-cat-file -t $newrev)
+fi
 
 case "$refname","$newrev_type" in
 	refs/tags/*,commit)