EVR: Don't repaint with black until the surface is active

A frame must be presented until pause/play is called.

Fixes tst_QMediaPlayerBackend::seekPauseSeek

Task-number: QTBUG-65574
Change-Id: I6946c5a5977c44fed80abce364a4222845898016
Reviewed-by: Christian Strømme <christian.stromme@qt.io>