qdbuscpp2xml: Fixed wrong filename being reported in messages

This caused the filename in messages to be one of the other arguments
that were specified instead of the actual filename.

Caused by the fact that mutations are possibly made to `args` in
`parseCmdLine` and thus the amount of items in `args` does not always
match the amount of items in `argv`.

Change-Id: Ief3716dde39dfdc949a5192e7f83d93cf90130f0
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/tools/qdbuscpp2xml/qdbuscpp2xml.cpp

@@ -420,7 +420,7 @@ int main(int argc, char **argv)
         pp.macros["Q_MOC_RUN"];
         pp.macros["__cplusplus"];
 
-        const QByteArray filename = QFile::decodeName(argv[i]).toLatin1();
+        const QByteArray filename = arg.toLocal8Bit();
 
         moc.filename = filename;
         moc.currentFilenames.push(filename);