lts-release-mail: Handle commits with multiple Change-Id lines

Some commits (dependabot specifically) appear to have 2 Change-Id
lines in the commit description, and one which belongs to the TF
Gerrit is actually the last one. So, rework Change-Id parsing to
handle such cases.

Addresses https://linaro.atlassian.net/browse/TFC-692

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: Ia6bb60e2490ac72ac0aeead3bc8571d14f8a00da
diff --git a/lts/lts-release-mail.py b/lts/lts-release-mail.py
index 13ee2ff..e5268f7 100755
--- a/lts/lts-release-mail.py
+++ b/lts/lts-release-mail.py
@@ -89,10 +89,14 @@
     urls = []
     for s in subjects:
         commit_id, _ = s.split(" ", 1)
+        change_id = None
         for l in os.popen("git show %s" % commit_id):
+            # There can be multiple Change-Id lines in some commits, and
+            # we're interested in the last in that case.
             if "Change-Id:" in l:
                 _, change_id = l.strip().split(None, 1)
-                urls.append("https://review.trustedfirmware.org/q/" + change_id)
+        if change_id:
+            urls.append("https://review.trustedfirmware.org/q/" + change_id)
 
     assert len(subjects) == len(urls)