[libcalamaresui] if there's a YAML exception in branding, bail

- all kinds of type errors result in bailing out, but a totally
   broken branding file does not?

src/libcalamaresui/Branding.cpp

@@ -197,6 +197,7 @@ Branding::Branding( const QString& brandingFilePath,
         catch ( YAML::Exception& e )
         {
             CalamaresUtils::explainYamlException( e, ba, file.fileName() );
+            bail( e.what() );
         }
 
         QDir translationsDir( componentDir.filePath( "lang" ) );