Fix: prevent call to deleted condition_variable
Fix: prevent call to deleted condition_variable

- https://github.com/tangrams/tangram-es/issues/1773

cleeus/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,tangrams/tangram-es,cleeus/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es