Test Only - MasterLocale not part of Target Site

Steps to reproduce

1. create site A:
   1. default lang & fallback lang = fr,
   2. i18n langs = en, fr
2. create site B:
   1. default lang & fallbacklang = es,
   2. i18n langs = en, es
   3. masterlocale = fr
3. try to fetch the fallback locale:
   1. info.magnolia.livecopy.i18n.LiveCopyI18nContentSupport#getFallbackLocale (Version 3.2.3)
4. the fallback locale returns fr instead of es, also for pages w/o fr content. 

Expected results

The fallback locale shoud only be the master locale, if those exists. if it's not, the default locale (aka fallback locale) should be returned. 

Actual results

once the master locale is set, the fallback locale is ignored. 

Workaround

n/a

Development notes

1. Test at info.magnolia.livecopy.i18n.LiveCopyI18nContentSupport#getFallbackLocale if masterlocale is part of current site. 
2. if yes: return masterlocale
3. if not: return fallback locale
4.  this has impact on the edit mode