translations: Don't default new translated strings to empty

Empty strings are apparently passed through to the UI, which is a worse experience than just showing the English version of untranslated strings.

Weblate can also highlight strings where the source == translated, so at least that's something.

.bartycrouch.toml

@@ -10,7 +10,7 @@ unstripped = false
 [update.code]
 codePaths = ["."]
 localizablePaths = ["."]
-defaultToKeys = false
+defaultToKeys = true
 additive = false
 unstripped = false