Adding unit test for topo empty files.
Adding unit test for topo empty files.

As proto-encoding of empty structures yeilds an empty byte array, this
is an important test case to cover.

mattharden/vitess,rnavarro/vitess,vitessio/vitess,mahak/vitess,dcadevil/vitess,rnavarro/vitess,applift/vitess,mattharden/vitess,rnavarro/vitess,vitessio/vitess,applift/vitess,enisoc/vitess,pivanof/vitess,dcadevil/vitess,HubSpot/vitess,enisoc/vitess,alainjobart/vitess,tirsen/vitess,HubSpot/vitess,tinyspeck/vitess,mattharden/vitess,HubSpot/vitess,mattharden/vitess,alainjobart/vitess,mattharden/vitess,tirsen/vitess,pivanof/vitess,dcadevil/vitess,enisoc/vitess,sougou/vitess,applift/vitess,tirsen/vitess,enisoc/vitess,pivanof/vitess,sougou/vitess,alainjobart/vitess,tirsen/vitess,pivanof/vitess,rnavarro/vitess,dcadevil/vitess,pivanof/vitess,alainjobart/vitess,pivanof/vitess,HubSpot/vitess,rnavarro/vitess,davygeek/vitess,vitessio/vitess,vitessio/vitess,HubSpot/vitess,tinyspeck/vitess,mahak/vitess,mahak/vitess,mahak/vitess,pivanof/vitess,dcadevil/vitess,HubSpot/vitess,rnavarro/vitess,enisoc/vitess,applift/vitess,tirsen/vitess,davygeek/vitess,vitessio/vitess,dcadevil/vitess,alainjobart/vitess,pivanof/vitess,tinyspeck/vitess,applift/vitess,davygeek/vitess,rnavarro/vitess,alainjobart/vitess,sougou/vitess,tinyspeck/vitess,tirsen/vitess,vitessio/vitess,mattharden/vitess,tinyspeck/vitess,davygeek/vitess,HubSpot/vitess,mattharden/vitess,dcadevil/vitess,HubSpot/vitess,alainjobart/vitess,sougou/vitess,mahak/vitess,tirsen/vitess,enisoc/vitess,tirsen/vitess,applift/vitess,rnavarro/vitess,sougou/vitess,applift/vitess,pivanof/vitess,sougou/vitess,sougou/vitess,mattharden/vitess,enisoc/vitess,davygeek/vitess,tinyspeck/vitess,vitessio/vitess,mattharden/vitess,davygeek/vitess,mattharden/vitess,applift/vitess,mahak/vitess,alainjobart/vitess,applift/vitess,sougou/vitess,mahak/vitess,tinyspeck/vitess,tirsen/vitess,applift/vitess,mahak/vitess,vitessio/vitess,davygeek/vitess,rnavarro/vitess