Fix for setPosition in QMediaPlayer's asynchronous API

Qt 5.1 seems to have all sorts of issues with getting metadata properly (it either shows everything blank, or randomly switches out some valid data for empty data).  Qt 5.2 fixes this, but also requires calls to setPosition to occur at the right time due to its async API.  Additionally, fStartTime was getting re-assigned every time the play button was pressed, causing it to be incorrect even if setPosition worked properly in its old location.