[2.9] 'Learn more' button link resolves to an undefined page

[Eugene-Savenko]

It resolves here: https://m.adguard.com/ru/%7B0%7D/purchase.html

STR:

1. Try to activate the app with and expired key:

2. Click Learn more:

3. See this:

[Revertron]

Fixed, review AJC-CR-199