git-fetch --update-head-ok typofix

Martin Waitz noticed that one of the case arms had an impossible
choice.  It turns out that what it was checking was redundant and
the typo did not have any effect.
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-fetch.sh

@@ -436,10 +436,10 @@ esac
 
 # If the original head was empty (i.e. no "master" yet), or
 # if we were told not to worry, we do not have to check.
-case ",$update_head_ok,$orig_head," in
-*,, | t,* )
+case "$orig_head" in
+'')
 	;;
-*)
+?*)
 	curr_head=$(git-rev-parse --verify HEAD 2>/dev/null)
 	if test "$curr_head" != "$orig_head"
 	then