default ctor LangID acutally is initialized

So make registerImpl() use theDontKnow instead of creating temporary
instances.

Change-Id: Ibd10a80da5dd4355c33cf525b21158ec56a1360e

i18nlangtag/source/languagetag/languagetag.cxx

@@ -499,7 +499,7 @@ LanguageTag::LanguageTag()
         mbSystemLocale( false),
         mbInitializedBcp47( false),
         mbInitializedLocale( false),
-        mbInitializedLangID( false),
+        mbInitializedLangID( true),
         mbIsFallback( false)
 {
 }