fix: restore functionality to offer to install elan

[semorrison]

No description provided.

[bryangingechen]

The idea behind setting hasLean = true there was to prevent the "install elan" dialogue from popping up unnecessarily (see #95). Ideally it should be at the first location in the code which is unreachable unless a working copy of lean is present (for example, I had thought that if there was no working lean, then by this point execution will have passed to the catch block). Where it is now seems to be too early since it prevents the dialog from ever showing up. It could be that this is the wrong approach entirely, but if not, can you check to see if putting that line later on in that block works better?

[gebner]

Merging this now since I'm going on vacation tomorrow. Feel free to submit another PR that fixes this properly.