InfoLabels: initialise return value in timeToSecs to fix a python exception if an invalid/unexpected h:m:s array is passed

This was discovered when using the tuxbox functionality - when playing a stream, for some unknown reason the Player.Duration label doesn't return a h:m:s value anymore, but rather a string like "Length: 90 Minutes (11:45 - 13:15)", which initially gets split by the colons into four parts, which in turn isn't handled by the timeToSecs function (such a time representation would probably be invalid, anyway). This resulted in currentSecs being returned uninitialised, causing an exception.