Ignore .!qB when extracting file extensions

Do you mean something like the following?
```CPP
  QString name = QString(filename);
  if (name.endsWith(".!qB"))
    name.chop(4);
  const int point_index = name.lastIndexOf(".");
  return (point_index >= 0) ? name.mid(point_index + 1) : QString();
```
I opted for ```remove()``` because it doesn't matter if stuff before the (real) file extension is removed (which is unlikely given what we are removing) and made the code simpler.