Instead of returning null, LfsProtocolServlet#getLargeFileRepository
should throw LfsUnavailable.
If null is returned, throw a generic LfsException.
Handle LfsException as an internal server error and return HTTP 500.
Change-Id: I33e2a19fcc0fde8aaf0f703860c8fa8ce2de2db5
Signed-off-by: David Pursehouse <david.pursehouse@gmail.com>