`navigate()` falls through to window.location on no matching route.

Per previous conversations with @ericf.
If this looks like an acceptable solution, I can add tests.

/cc @pdokas @jeremyruppel
What’s the right thing to do here? The docs say “`true` if the URL was navigated to, `false` otherwise.” On one hand, the browser *is* winding up at the URL requested, but on the other it’s ultimately doing it without executing a route. I suppose if push came to shove I’d vote that it should return `true` if it assigns via `win.location`, but I can see the argument for `false`.