Theme configuration with backend not being taken into account

Between cc2519b3..83189d9d (correct gitlab link: cc2519b3...83189d9d 🙄) loading the theme name from both /api/pleroma/frontend_configurations and /static/config.json got broken.

At least on my instance:

• /api/pleroma/frontend_configurations points to wavemaster (correct theme, and a v2 theme)
• /static/config.json points to monokai-cybre (my old custom v1 theme, forgot about it…)

Got: Pleroma Dark theme gets loaded
Expected: wavemaster theme gets loaded