security-group show: fix empty response if an API endpoint is misbehaving (#660)

# Description
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`exo compute security-group show` iterates through all zones to retrieve
instances associated with it. If a single API endpoint happened to throw
an error, the call itself would error out. This fix allows showing that
security group while still showing an error

## Checklist
(For exoscale contributors)

* [x] Changelog updated (under *Unreleased* block)
* [x] Testing

## Testing

<!--
Describe the tests you did
-->

```
➜  ~/exo/cli git:(tgrondier/sc-114869/exo-c-sh-show-error-in-preprod) ✗ go run . c sg show edc0d129-2f94-4531-920e-7cf798439cd3                                                                                             25-01-06 16:40 
error while listing instances in security group: 1 error occurred:
        * Get "https://ppapi-at-vie-2.exoscale.com/v2/instance": dial tcp: lookup ppapi-at-vie-2.exoscale.com on 127.0.0.53:53: server misbehaving

┼──────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼
│  SECURITY GROUP  │                                                                                                                 │
┼──────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼
│ ID               │ edc0d129-2f94-4531-920e-7cf798439cd3                                                                            │
│ Name             │ default                                                                                                         │
│ Description      │ Default Security Group                                                                                          │
│ Ingress Rules    │                                                                                                                 │
│                  │   08798387-0c7d-4601-a5ed-93367b889314      TCP   0.0.0.0/0   22                                                │
│                  │                                                                                                                 │
│ Egress Rules     │ -                                                                                                               │
│ External Sources │ -                                                                                                               │
│ Instances        │                                                                                                                 │
│                  │   VM-ec365352-f303-4fac-9cad-26e4a63b2227   ec365352-f303-4fac-9cad-26e4a63b2227   159.100.241.234   ch-gva-2   │
│                  │   VM-79e75e58-34c8-4f99-8168-e37722eb97cc   79e75e58-34c8-4f99-8168-e37722eb97cc   85.217.161.242    ch-gva-2   │
│                  │   VM-33e1fdda-d1d4-4fbd-8c7a-4e49971e3975   33e1fdda-d1d4-4fbd-8c7a-4e49971e3975   85.217.161.235    ch-gva-2   │
│                  │                                                                                                                 │
┼──────────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼

```

Author: tgrondier

CHANGELOG.md

@@ -11,6 +11,7 @@
 
 - instance update: fixing no err check after creating client #657
 - fix(error): Improve error message on snapshot creation (#655)
+- security-group show: fix empty response if an API endpoint is misbehaving #660
 
 ## 1.82.0
 

utils/utils.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"crypto/rand"
 	"encoding/base64"
+	"errors"
 	"fmt"
 	"net"
 	"strconv"
@@ -49,15 +50,21 @@ func GetInstancesInSecurityGroup(ctx context.Context, client *v2.Client, securit
 
 		instances, err := client.ListInstances(ctx, zone)
 		if err != nil {
-			return err
+			if !errors.Is(err, exoapi.ErrNotFound) {
+				return err
+			}
+		} else {
+			allInstances = append(allInstances, instances...)
 		}
 
-		allInstances = append(allInstances, instances...)
-
 		return nil
 	})
 	if err != nil {
-		return nil, err
+		if allInstances == nil {
+			return nil, err
+		} else {
+			fmt.Printf("error while listing instances in security group: %s", err)
+		}
 	}
 
 	var instancesInSG []*v2.Instance