Simplify GetAllCredentials

In the exec.ErrNotFound case, set creds to nil
so that we have the ordinary handling on the main
line.

Then eliminate two consecutive if statements with the same
condition.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

pkg/docker/config/config.go

@@ -171,17 +171,14 @@ func GetAllCredentials(sys *types.SystemContext) (map[string]types.DockerAuthCon
 			creds, err := listAuthsFromCredHelper(helper)
 			if err != nil {
 				logrus.Debugf("Error listing credentials stored in credential helper %s: %v", helper, err)
-			}
-			if err != nil {
 				if errors.Is(err, exec.ErrNotFound) {
-					// It's okay if the helper doesn't exist.
+					creds = nil // It's okay if the helper doesn't exist.
 				} else {
 					return nil, err
 				}
-			} else {
-				for registry := range creds {
-					addKey(registry)
-				}
+			}
+			for registry := range creds {
+				addKey(registry)
 			}
 		}
 	}