Fixed player errors when the plugin was supplied with invalid
float values (i.e. NaN) and ensured that scrubbing is only
attempted with the media elements readyState > 2, e.g.:

3 = HAVE_FUTURE_DATA - data for the current and at least the next frame is available
4 = HAVE_ENOUGH_DATA - enough data available to start playing.

Otherwise, e.g.:

0 = HAVE_NOTHING - no information whether or not the audio/video is ready
1 = HAVE_METADATA - metadata for the audio/video is ready
2 = HAVE_CURRENT_DATA - data for the current playback position is available, but not enough data to play next frame/millisecond.

... The time set is skipped, but will be performed on the next
frame after readyState exceeds 2, that is to say: It's not
forgotten.