ez: Fix 'trailers -F' used on a single commit

Running 'b4 trailers -u -F <msgid>' on a single commit fails:

CRITICAL: Failed to convert range to patches: Could not run rev-list None~1..409ee53c38a1d9a60e76ffa92088cfad07cea850

The problem is the loop is exited after 1 iteration and prevcommit is never
set.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://msgid.link/20230330201529.2744290-1-robh@kernel.org
Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/b4/ez.py b/b4/ez.py
index d0c0667..fdb7d88 100644
--- a/b4/ez.py
+++ b/b4/ez.py
@@ -834,6 +834,8 @@ def update_trailers(cmdargs: argparse.Namespace) -> None:
                 break
             prevparent = parent
             prevcommit = commit
+        if prevcommit is None:
+            prevcommit = end
         start = f'{prevcommit}~1'
     else:
         logger.critical('CRITICAL: Please specify -F msgid to look up trailers from remote.')