Test that no event is emitted when withdraw fails

[Glittersup]

Summary

A Withdrawn event published for a withdrawal that did not happen would cause an indexer to credit a recipient incorrectly. The failure path is tested for its error but not for the absence of an event.

Acceptance criteria

• A test asserts no Withdrawn event is published when withdraw fails.
• The test covers the case where nothing has vested yet.
• The suite still passes.

Getting started

Fork this repository, clone your fork, and add this repo as upstream:

git clone https://github.com/<your-username>/tricklepay-contracts.git
cd tricklepay-contracts
git remote add upstream https://github.com/TricklePay/tricklepay-contracts.git

Create a branch for this issue:

git checkout -b test/issue-179

Suggested commit message:

test: assert no event on failed withdraw

Run cargo fmt --check, cargo clippy --all-targets -- -D warnings, and cargo test before opening a pull request and linking this issue.