DirectShow: Add warning when not supported playback rate applied

IMediaSeeking::SetRate() may return an error when not supported rate is
being applied.
Added a warning to inform user about incorrect rate value
also fixed a bug when the rate has been always fell back to 1.0
instead of previous value.

Task-number: QTBUG-55354
Change-Id: I85fb5572cba6920b461a023aef1bc09a981ab033
Reviewed-by: Christian Stromme <christian.stromme@qt.io>