Don't crash on absent cover letter

We may not have an lmsg[0], so check for that.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

1 files changed, 1 insertions, 1 deletions

diff --git a/b4/mbox.py b/b4/mbox.py
index 337875b..de2cfc6 100644
--- a/b4/mbox.py
+++ b/b4/mbox.py
@@ -152,7 +152,7 @@ def make_am(msgs, cmdargs, msgid):
         warned = False
         for lmsg in lser.patches:
             # Only check cover letter or first patch
-            if lmsg.counter > 1:
+            if not lmsg or lmsg.counter > 1:
                 continue
             for trailer in list(lmsg.followup_trailers):
                 if trailer[0].lower() == 'obsoleted-by':