Importing settings json from v5.1.7 irreparably corrupts settings

[tamius-han]

Describe the bug
If you export Ultrawidify settings from 5.1.7 into 6.3.0 (and likely older), settings get irreversably corrupted.

To Reproduce

1. Export Ultrawidify settings from Firefox, where Ultrawidify is still at 5.1.7
2. Import those settings into Ultrawidify 6.3.0

Expected behavior
Settings get migrated and extension gets launched.

Actual result
Settings don't appear to get migrated correctly, which causes extension to crash during initialziation.

Browser and OS

• Browser: Chrome 137.0.7151.120
• Operating system: Windows 10
• Ultrawidify version: 6.3.0

Additional info

• CWS users should be on v6.0 since five-ever now, so this probably isn't too big of a deal for Chrome releases. (Though — could This version (6.2.4) doesn't work at all (or maybe I'm stupid idk) #268 be related to this? It shouldn't be, as Ultrawidify settings got force-reset on migration for a few months after initial v6.2.x release)
• This NEEDS to be fixed BEFORE releasing Firefox and Edge version of this addon (No New Version Update on Microsoft Add-ons Store #282)