Fix unhandled exception when locale specifies unknown country/region code.

[ghost]

In some cases an unknown country code is obtained from the locale. According to the documentation, country code is "ISO 3166 alpha-2 country code or UN M.49 numeric-3 area code" (e.g. 419 = Spanish in Latin America and the Caribbean). Bisq uses the country code to choose the "Default Currency" setting for new users, but if a region is specified instead, we cannot determine the currency automatically.

• PRE: If the country code was unknown we would get an exception resulting in a blank screen and no app start up.
• POST: Locale setting will be logged at startup.
• POST: If the country code is unknown the default currency will fallback to USD and startup will continue normally.
• Language preference will still come from the locale setting.

Fixes #5877
Ref: #1204

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Example:

INFO  b.core.locale.GlobalSettings: Locale info: es_419

WARN  bisq.core.user.Preferences: Could not determine currency for country 419 [java.lang.IllegalArgumentException] 

[ghost]

utACK

[ripcurlx]

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