promise<T...>::require_anonymous() should require that the dependency count of the promise is greater than 0

[Amir Kamil]

Otherwise, a promise can be taken from a fulfilled to an unfulfilled state. Promise-based communication ops already explicitly require that the promise's dependency count be greater than 0, but require_anonymous() is missing this requirement.

[Amir Kamil]

Fix Issue #84: promise<T...>::require_anonymous() should require that the dependency count of the promise is greater than 0.

→ <<cset 880ea27f1b85>>