Go back to previous page after login

[alectrocute]

Hey everybody! Proposal:

• Let's check history.action is PUSH (eg. there's some Lemmy page to go back to) and if so, use History API to go back() upon successful login. This will resolve When you log in, it kicks you back into the front page, losing where you were and disorienting the user #1268.

Also included bugfix:

• Fix a bug, a pretty bad one, that became very noticeable while testing this feature. It prevents the user from navigating to / from /login, if /login is the first loaded page in that browser tab. I don't know if this is reported. Checking if this.isoData.routeData.length is falsey and some optional chaining fixes this right up. This only affects >= 0.18 and seems to be related to the HTTP migration.

bug.mov

Reproduction steps:

• Open Incognito window to <localhost:1234>/login
• Click on main title on navbar, or login, to navigate to /.
• Notice the page doesn't change and error occurs in console.