Fix nil-ponter in TUI

[kotakanbe]

$ ./vuls tui
INFO[0000] Validating config...
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4132d06]

goroutine 1 [running]:
panic(0x4710bc0, 0xc4200121b0)
        /usr/local/go/src/runtime/panic.go:500 +0x1a1
github.com/future-architect/vuls/vendor/github.com/Sirupsen/logrus.(*Entry).Debugf(0x0, 0x47c980a, 0x1b, 0xc42017ce30, 0x1, 0x1)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/vendor/github.com/Sirupsen/logrus/entry.go:177 +0x26
github.com/future-architect/vuls/cveapi.cvedictClient.FetchCveDetailsFromCveDB(0x0, 0x0, 0xc42036c580, 0x5, 0x8, 0xc42017d418, 0x6, 0x4, 0xc4200001a0, 0x0)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/cveapi/cve_client.go:137 +0xcd
github.com/future-architect/vuls/cveapi.cvedictClient.FetchCveDetails(0x0, 0x0, 0xc42036c580, 0x5, 0x8, 0x0, 0x0, 0x0, 0x0, 0x0)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/cveapi/cve_client.go:75 +0xd6f
github.com/future-architect/vuls/models.ScanResult.FillCveDetail(0xed05c3e95, 0x3b978fe3, 0x4b28460, 0x0, 0x0, 0xc420370450, 0xb, 0xc42037044c, 0x4, 0xc420370460, ...)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/models/models.go:90 +0x353
github.com/future-architect/vuls/commands.fillCveInfoFromCveDB(0xed05c3e95, 0x3b978fe3, 0x4b28460, 0x0, 0x0, 0xc420370450, 0xb, 0xc42037044c, 0x4, 0xc420370460, ...)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/commands/util.go:170 +0x168
github.com/future-architect/vuls/commands.(*TuiCmd).Execute(0xc420367f80, 0x4af3140, 0xc4200123c0, 0xc420315980, 0x0, 0x0, 0x0, 0x1)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/commands/tui.go:147 +0x4c6
github.com/future-architect/vuls/vendor/github.com/google/subcommands.(*Commander).Execute(0xc420058070, 0x4af3140, 0xc4200123c0, 0x0, 0x0, 0x0, 0x0)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/vendor/github.com/google/subcommands/subcommands.go:141 +0x3a7
github.com/future-architect/vuls/vendor/github.com/google/subcommands.Execute(0x4af3140, 0xc4200123c0, 0x0, 0x0, 0x0, 0xc420370130)
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/vendor/github.com/google/subcommands/subcommands.go:371 +0x5f
main.main()
        /Users/kotakanbe/go/src/github.com/future-architect/vuls/main.go:58 +0x361

What did you implement:

Closes #384

How did you implement it:

Initialize util.Log

How can we verify it:

./vuls tui

Todos:

You don't have to satisfy all of the following.

• Write tests
• Write documentation
• Check that there aren't other open pull requests for the same issue/feature
• Format your source code by make fmt
• Pass the test by make test
• Provide verification config / commands
• Enable "Allow edits from maintainers" for this PR
• Update the messages below

Is this ready for review?: NO
Is it a breaking change?: NO