We should:

1. Atomically create the IPFS_HOME/api file to ensure we never leave an empty/corrupt one behind. The relevant code is in the SetAPIAddr function in repo/fsrepo/fsrepo.go. We should create a temporary file, write to the temporary file, then atomically rename to "api".
2. If we read the "api" file and it's empty, we should ignore it.

Reported on the forums: https://discuss.ipfs.io/t/error-multiaddr-must-start-with-a/7824