Better failure mode for missing pickle key / keytar

### Steps to reproduce

1. Download element-desktop normal distribution & log in
2. Build your own element-desktop without the native node modules & run it

### What happened?

### What did you expect?
Probably an error of some kind, maybe explaining that the native module hasn't loaded and so we can't access your secrets and load your account.

### What happened?
Element loads but with the 'offline' banner at the bottom, because it is sending, "[Object object]" as an access token in the Authorization header because the keytar module isn't available and so it can't get the pickle key to decrypt the access token, so it just uses the result straight out of the database, which is an object.

### Operating system

_No response_

### Application version

_No response_

### How did you install the app?

_No response_

### Homeserver

_No response_

### Have you submitted a rageshake?

No