upnp: add some potentially useful logging to CUPnPPlayer::PlayFile()

Since one of the new features of Gotham is the "Play using..." over UPnP we get quite a few reports of cases where it doesn't work for one reason or another. Unfortunately our logging in CUPnPPlayer::PlayFile() is very scarce and it is impossible to find out where it exactly failed and if it is a XBMC bug or an inconsistency in the UPnP renderer implementation of the target (which can be a non-XBMC device). Therefore I've decided to add some logging that at least tells us which call/request failed (no details on the why but at least we know where).