git-merge: fix "fix confusion between tag and branch" for real

An earlier commit 3683dc5a broke the merge message generation with
a careless use of && where it was not needed, breaking the merge
message for cases where non branches are given.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-merge.sh

@@ -188,8 +188,9 @@ else
 	# in this loop.
 	merge_name=$(for remote
 		do
-			rh=$(git-rev-parse --verify "$remote"^0 2>/dev/null) &&
-			bh=$(git show-ref -s --verify "refs/heads/$remote" 2>/dev/null) &&
+			rh=$(git-rev-parse --verify "$remote"^0 2>/dev/null) ||
+			continue ;# not something we can merge
+			bh=$(git show-ref -s --verify "refs/heads/$remote" 2>/dev/null)
 			if test "$rh" = "$bh"
 			then
 				echo "$rh		branch '$remote' of ."