sample commit-msg hook: no silent exit on duplicate Signed-off-by lines

git-commit would silently exit if duplicate Signed-off-by
lines were found.  Users of git-commit would not know it,
unless they checked '$?'.  This patch makes git-commit
actually print out a message that nothing was commited
since duplicate Signed-off-lines were found.

Signed-off-by: Luben Tuikov <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ltuikov

templates/hooks--commit-msg

@@ -11,4 +11,8 @@
 # This example catches duplicate Signed-off-by lines.
 
 test "" = "$(grep '^Signed-off-by: ' "$1" |
-	 sort | uniq -c | sed -e '/^[ 	]*1[ 	]/d')"
+	 sort | uniq -c | sed -e '/^[ 	]*1[ 	]/d')" || {
+	echo >&2 Duplicate Signed-off-by lines.
+	exit 1
+}
+