dep crush on status -dot

[gregory-m]

In case status can't output version see #664

dep status -dot panics:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x48 pc=0x13b757e]

goroutine 1 [running]:
main.(*dotOutput).BasicLine(0xc420199ce0, 0xc4201b61c0)
	/Users/gregory/Documents/gospace/src/github.com/golang/dep/cmd/dep/status.go:177 +0x2e
main.runStatusAll(0xc42013b9c0, 0x1680c00, 0xc420199ce0, 0xc420135080, 0x1682280, 0xc42001df80, 0x0, 0x1)
	/Users/gregory/Documents/gospace/src/github.com/golang/dep/cmd/dep/status.go:359 +0x8a4
main.(*statusCommand).Run(0xc420134d20, 0xc42013d9c0, 0xc4200102f0, 0x0, 0x0, 0x0, 0x0)
	/Users/gregory/Documents/gospace/src/github.com/golang/dep/cmd/dep/status.go:218 +0x1f2
main.(*Config).Run(0xc42001cfc0, 0xc42001cfc0)
	/Users/gregory/Documents/gospace/src/github.com/golang/dep/cmd/dep/main.go:161 +0x8e3
main.main()
	/Users/gregory/Documents/gospace/src/github.com/golang/dep/cmd/dep/main.go:44 +0x253

[darkowlzz]

@gregory-m thanks for reporting.

Adding some more info:
I'm able to reproduce it by editing manifest and running ensure, same steps as in #664 .
-dot works fine before any manual changes to manifest. Panics after changing and running ensure.

[gregory-m]

I think it good idea to check if version is not null.
Any objections?

[darkowlzz]

@gregory-m yeah, checking for version to be nil and falling back to revision should be good.

Also, when we use revision, maybe we should shorten the revision, at least for the git rev hashes?
Because this

would look weird and I don't think people would use the full rev hash from the image.

IMO, this looks much better.

@sdboyer @carolynvs opinions?

[sdboyer]

Yep, shortening would be ideal. Looks like we have the formatVersion() func to do that.

[gregory-m]

Ok, I will do it.