Reading certain certificates can cause a panic

[Brcrwilliams]

This cert causes a panic

-----BEGIN CERTIFICATE-----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-----END CERTIFICATE-----

example trace:

x509meta --pem root_certificate.pem
panic: runtime error: slice bounds out of range [-2:]

goroutine 1 [running]:
github.com/brcrwilliams/tlstools.encodeColonSeparatedHex({0x0, 0x0, 0x0})
        /Users/bwilliams/git/tlstools/openssl.go:344 +0x345
github.com/brcrwilliams/tlstools.newX509v3Extensions(0xc000148000)
        /Users/bwilliams/git/tlstools/openssl.go:208 +0x3a5
github.com/brcrwilliams/tlstools.CertToOpenSSL(0xc000148000)
        /Users/bwilliams/git/tlstools/openssl.go:39 +0x2a5
github.com/brcrwilliams/tlstools.WriteX509Metas({0x12ffe60, 0xc000010018}, {0xc000010050, 0x1, 0x4})
        /Users/bwilliams/git/tlstools/writer.go:27 +0x9f
github.com/brcrwilliams/tlstools/cmd/x509meta/cli.getPEM({0x7ff7bfeff707, 0xc000138100})
        /Users/bwilliams/git/tlstools/cmd/x509meta/cli/cli.go:106 +0xe7
github.com/brcrwilliams/tlstools/cmd/x509meta/cli.NewCommand.func1(0xc000014840, {0x12a34ba, 0x2, 0x2})
        /Users/bwilliams/git/tlstools/cmd/x509meta/cli/cli.go:51 +0xc7
github.com/spf13/cobra.(*Command).execute(0xc000014840, {0xc0000120d0, 0x2, 0x2})
        /Users/bwilliams/.asdf/installs/golang/1.17.2/packages/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:842 +0x60e
github.com/spf13/cobra.(*Command).ExecuteC(0xc000014840)
        /Users/bwilliams/.asdf/installs/golang/1.17.2/packages/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:950 +0x3ad
github.com/spf13/cobra.(*Command).Execute(...)
        /Users/bwilliams/.asdf/installs/golang/1.17.2/packages/pkg/mod/github.com/spf13/cobra@v1.0.0/command.go:887
main.main()
        /Users/bwilliams/git/tlstools/cmd/x509meta/main.go:10 +0x1e