new: [compose-core] output traceable error when list of services are not available in ``_service:all:relations_cached``

bin/compose-core

@@ -3215,7 +3215,10 @@ get_all_compose_yml_service() {
 ## Outputs all relations array.
 _service:all:relations_cached() {
     local services service E
-    services=($(compose:yml:root:services)) || return 1
+    services=($(compose:yml:root:services)) || {
+        err-d "Failed to get services from compose yml."
+        return 1
+    }
     get_all_relations "${services[@]}" || return 1
 }