Fix invalid characters count in QBig5hkscsCodec::convertFromUnicode()

Change-Id: I3b06361f93e7ab6a3336b2c432e0a163a34ccb43
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>
Reviewed-by: Liang Qi <liang.qi@theqtcompany.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>

src/corelib/codecs/qbig5codec.cpp

@@ -1913,6 +1913,7 @@ QByteArray QBig5hkscsCodec::convertFromUnicode(const QChar *uc, int len, Convert
         } else {
             // Error
             *cursor++ = replacement;
+            ++invalid;
         }
     }
     rstr.resize(cursor - (uchar*)rstr.constData());