Issue:
If a job somehow loses its BranchJobProperty in its config.xml via adjusting properties or something similar, it is unable to recover without massive manual intervention

Steps to reproduce:
1. Create a multibranch job with at least one branch containing a Jenkinsfile
2. Do a branch indexing event on that multibranch job
3. Edit the config.xml to remove the BranchJobProperty
4. Restart Jenkins
5. Observe the branch will no longer show up in the multibranch project and it is unable to be corrected via a branch indexing event

Steps to workaround:
1. Completely remove the config.xml on the filesystem
2. Restart Jenkins
3. Re-trigger an indexing event

We should most likely handle issues like this more gracefully/automatically