frint-router: improve test coverage

Current coverage report:

```
$ (cd ./packages/frint-router && npm run cover:report)

---------------------------|----------|----------|----------|----------|----------------|
File | % Stmts | % Branch | % Funcs | % Lines |Uncovered Lines |
---------------------------|----------|----------|----------|----------|----------------|
All files | 98.76 | 82.35 | 100 | 98.73 | |
makeRouterService.js | 100 | 85 | 100 | 100 | 53,76 |
makeRouterService.spec.js | 100 | 100 | 100 | 100 | |
matchFromHistory.js | 89.47 | 78.57 | 100 | 88.89 | 6,30 |
matchFromHistory.spec.js | 100 | 100 | 100 | 100 | |
---------------------------|----------|----------|----------|----------|----------------|
```

Run the coverage command from the issue in packages/frint-router, then inspect makeRouterService.js lines 53 and 76 and matchFromHistory.js lines 6 and 30. Read the corresponding .spec.js files to follow existing test patterns. Done means the uncovered lines are exercised and the coverage report improves.

Written by the indexing model from the issue text.