Released browser lock on getTokenSilently error

[stevehobbsdev]

Description

This PR ensures that the browser lock is released if getTokenSilently encounters an error. Without this, a potential delay of 5 seconds is introduced between calls could occur during silent authentication as the lock is not released.

References

Fixes #275

Testing

Steps to reproduce:

• When the test page loads, open dev tools
• Click "Get access token with no interaction"
• Note that an Uncaught (in promise) "login_required" error is logged to the console almost immediately.
• Click "Get access token with no interaction" again
• The second time, it will (normally, see below*) take around five seconds for the error to be logged to the console. There is also normally a TypeError: Cannot read property 'close' of undefined error logged alongside.

• This change adds test coverage for new/changed/fixed functionality

Checklist

• I have added documentation for new/changed functionality in this PR or in auth0.com/docs
• All active GitHub checks for tests, formatting, and security are passing
• The correct base branch is being used, if not master