tools: batch-rebase: Handle conflict while cherry picking last commit of topic
tools: batch-rebase: Handle conflict while cherry picking last commit of topic

The cherry-picking session will be finished by git when committing the conflict
resolution if that was the last commit of the topic. This will make a subsequent
`git cherry-pick --continue` fail, which can be safely ignored.

ARM-software/lisa,credp/lisa,ARM-software/lisa,credp/lisa,credp/lisa,credp/lisa,ARM-software/lisa,ARM-software/lisa