mossScope crashes when provided a non-moss directory

$ /dev/couchbase-server.spock/install/bin/mossScope stats footer not-a-moss-dir

panic: runtime error: slice bounds out of range

goroutine 1 [running]:

github.com/couchbase/moss.ParseFNameSeq(0xc420018955, 0x5, 0x11dfa1a, 0x5, 0xc420018a00)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/moss/store.go:429 +0xab

github.com/couchbase/moss.openStore(0x7fff5fbff99e, 0x24, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/moss/store.go:489 +0x220

github.com/couchbase/moss.OpenStore(0x7fff5fbff99e, 0x24, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/moss/store_api.go:214 +0x7a

github.com/couchbase/mossScope/cmd.invokeFooterStats(0xc420014b60, 0x1, 0x1, 0x0, 0x0)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/mossScope/cmd/footerStats.go:52 +0xd4

github.com/couchbase/mossScope/cmd.glob..func8(0x12cfc40, 0xc420014b60, 0x1, 0x1, 0x0, 0x0)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/mossScope/cmd/footerStats.go:41 +0x3f

github.com/spf13/cobra.(*Command).execute(0x12cfc40, 0xc420014b10, 0x1, 0x1, 0x12cfc40, 0xc420014b10)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/spf13/cobra/command.go:643 +0x3ef

github.com/spf13/cobra.(*Command).ExecuteC(0x12d06e0, 0xc42001c0b8, 0x0, 0x11772a4)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/spf13/cobra/command.go:734 +0x339

github.com/spf13/cobra.(*Command).Execute(0x12d06e0, 0x12d06e0, 0xc420051f50)

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/spf13/cobra/command.go:692 +0x2b

github.com/couchbase/mossScope/cmd.Execute()

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/mossScope/cmd/root.go:43 +0x31

main.main()

	/Users/steveyen/dev/couchbase-server.spock/godeps/src/github.com/couchbase/mossScope/main.go:20 +0x20