prevent panic accesing services in extended file

Signed-off-by: Nicolas De Loof <[email protected]>

loader/extends.go

@@ -163,8 +163,15 @@ func getExtendsBaseFromFile(
  if err != nil {
  return nil, nil, err
  }
- services := source["services"].(map[string]any)
- _, ok := services[ref]
+ m, ok := source["services"]
+ if !ok {
+ return nil, nil, fmt.Errorf("cannot extend service %q in %s: no services section", name, local)
+ }
+ services, ok := m.(map[string]any)
+ if !ok {
+ return nil, nil, fmt.Errorf("cannot extend service %q in %s: services must be a mapping", name, local)
+ }
+ _, ok = services[ref]
  if !ok {
  return nil, nil, fmt.Errorf(
  "cannot extend service %q in %s: service %q not found in %s",