[Trunk] load PDF without content-disposition header in musescore connect

I have noticed that I couldn't download and open a pdf from imslp.com directly like the connect.musescore.com does for scores. The problem is that the function which is responsible for creating the name of the file in the temp-folder only looks for one specific header, which may not exist for other replies than those of connect.musescore.com. The default-name was "unknown.mscz", which will not work for a pdf ofcourse.

The patch I've included is an updated version of MuseScore::networkFinished, that gets the name of the file out of the URL if it ends with ".pdf" or ".mscz". It should be able to open PDFs (if OMR is on) and MSCZs from other sites as well now.