Support projects with no root .gitproj (multiple subsidary .gitproj)

[kriscooke]

When running git project load from a non-root directory where a .gitproj is present but no .gitproj exists at the root level, it fails:

.gitproj file missing. Refer to the git-project readme

This occurred when we split the root .gitproj into multiple .gitproj separated by domain - making the root one redundant. However because of the above, the (empty) .gitproj could not be deleted.