fix config setup.

[arthuraliiev]

Description

when there is no config at all and you try to add a config, it returns a runtime error: invalid memory address or nil pointer dereference

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xa310e9]

goroutine 1 [running]:
github.com/exoscale/cli/cmd/config.promptAccountInformation()
    /cli/cmd/config/config_add.go:130 +0x849
github.com/exoscale/cli/cmd/config.addConfigAccount(0x0?)
    /cli/cmd/config/config_add.go:55 +0xab
github.com/exoscale/cli/cmd/config.configCmdRun(0x1739980, {0xf98a15?, 0x4?, 0xf98875?})
    /cli/cmd/config/config.go:75 +0x5ba
github.com/spf13/cobra.(*Command).execute(0x1739980, {0x176db20, 0x0, 0x0})
    /cli/vendor/github.com/spf13/cobra/command.go:856 +0x6aa
github.com/spf13/cobra.(*Command).ExecuteC(0x1735b00)
    /cli/vendor/github.com/spf13/cobra/command.go:974 +0x38d
github.com/spf13/cobra.(*Command).Execute(...)
    /cli/vendor/github.com/spf13/cobra/command.go:902
github.com/exoscale/cli/cmd.Execute({0xf97dd4?, 0x0?}, {0xf97dd7?, 0xc000002380?})
    /cli/cmd/root.go:81 +0x1d6
main.main()
    /cli/main.go:35 +0x3c
exit status 2

Checklist

(For exoscale contributors)

• Changelog updated (under Unreleased block)
• Testing

Testing

go run main.go config
No Exoscale CLI configuration found

In order to set up your configuration profile, you will need to retrieve
Exoscale API credentials from your organization's IAM:

    https://portal.exoscale.com/iam/keys

[+] API Key [none]: EXO
[+] Secret Key [none]: EydlkL
[+] Name [none]: test-config
Use the arrow keys to navigate: ↓ ↑ → ←
? Default zone:
  ▸ ch-gva-2
    ch-dk-2
    at-vie-1
    de-fra-1
    bg-sof-1
    de-muc-1
    at-vie-2
    hr-zag-1
    
 ===>>>
✔ ch-gva-2

====

go run main.go config
Use the arrow keys to navigate: ↓ ↑ → ←
? Configured accounts (* = default account):
  ▸ test-config*
    <Configure a new account>
    
===>>>
✔ test-config*

go run main.go compute security-group list
┼──────────────────────────────────────┼────────────────────┼────────────┼
│                  ID                  │        NAME        │ VISIBILITY │
┼──────────────────────────────────────┼────────────────────┼────────────┼
│ cd9f5925-4073-432c-9220-25e8436de58f │ default            │ private    │
│ a93f7361-26d7-4fad-98dc-d3890d528175 │ sks-security-group │ private    │
│ 6b745f48-5dd3-4148-8cbd-323cd99d2b86 │ ts                 │ private    │
│ 3fdec798-8858-401f-b62d-21d75a7e79f8 │ load-balancer-http │ private    │
│ fd0dd015-3c21-49b2-a035-087de4c0a35a │ iperf              │ private    │
│ b6ceec07-caa0-44d4-bd8b-30879becfc10 │ 443                │ private    │
│ 66e8a103-adf4-4573-8389-0cd0f79c9ca1 │ eighty             │ private    │
│ 38c0ab02-550a-4e97-986b-1189807c3bb6 │ 8444               │ private    │
│ 39d404f3-e0e8-4f48-a0f5-a174f80fe6e2 │ 8444_e             │ private    │
┼──────────────────────────────────────┼────────────────────┼────────────┼