git-merge: finish when git-read-tree fails

The message formating (commit v1.5.0.3-28-gbe242d57) broke the && chain.

Noticed by Dmitry Torokhov.
Signed-off-by: NSanti Béjar <sbejar@gmail.com>
Signed-off-by: NJunio C Hamano <junkio@cox.net>

git-merge.sh

@@ -292,13 +292,13 @@ f,*)
 	# Again the most common case of merging one remote.
 	echo "Updating $(git-rev-parse --short $head)..$(git-rev-parse --short $1)"
 	git-update-index --refresh 2>/dev/null
-	new_head=$(git-rev-parse --verify "$1^0") &&
-	git-read-tree -v -m -u --exclude-per-directory=.gitignore $head "$new_head" &&
 	msg="Fast forward"
 	if test -n "$have_message"
 	then
 		msg="$msg (no commit created; -m option ignored)"
 	fi
+	new_head=$(git-rev-parse --verify "$1^0") &&
+	git-read-tree -v -m -u --exclude-per-directory=.gitignore $head "$new_head" &&
 	finish "$new_head" "$msg" || exit
 	dropsave
 	exit 0