pw-apply: Trim leading dash from branch name

Otherwise git commands will fail badly, when the branch name matches
such pattern, e.g.:

  https://patchwork.kernel.org/user/todo/netdevbpf/?series=640543

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
diff --git a/pw-apply b/pw-apply
index 7c7b468..43cdb5d 100755
--- a/pw-apply
+++ b/pw-apply
@@ -39,6 +39,7 @@
              tr '[:upper:]' '[:lower:]' |
              tr -d '\n' |
              tr -cs '[:alnum:]_-' '-')
+  [ -n "$branch" -a ${branch:0:1} == '-' ] && branch=${branch:1}
   [ -n "$branch" -a ${branch: -1} == '-' ] && branch=${branch:: -1}
   cover_msgid=$(echo "$cover_json" | jq -r '.msgid' | tr -d '<>')
 }