for unknown locales check is needed even for ll[l][-CC] tag, fdo#86011 related

Found when investigating fdo#86011 where 'du-nl' was accepted and
assigned an on-the-fly-ID even if the 'du' language code is not defined
in ISO 639. If a tag is not internally known we need to check it using
liblangtag and take no short cut assuming it would be alright even not
for the simplest case.

Change-Id: Ib8c1eb77b6b4a59019c4c8248b596bf53c0f4986

i18nlangtag/source/languagetag/languagetag.cxx

@@ -1147,10 +1147,6 @@ bool LanguageTagImpl::canonicalize()
             convertLangToLocale();
         }
         if (mbInitializedLocale)
-        {
-            if (maLocale.Variant.isEmpty())
-                meIsLiblangtagNeeded = DECISION_NO;     // per definition ll[l][-CC]
-            else
         {
             if (!mbInitializedLangID)
             {
@@ -1166,7 +1162,6 @@ bool LanguageTagImpl::canonicalize()
                 if (rKnowns.find( maBcp47) != rKnowns.end())
                     meIsLiblangtagNeeded = DECISION_NO; // known fallback
             }
-            }
             // We may have an internal override "canonicalization".
             lang::Locale aNew( MsLangId::Conversion::getOverride( maLocale));
             if (!aNew.Language.isEmpty() &&