[WMF] Video position may exceed it's duration

Video position may exceed it's duration when "windows" backend is used.

This may happen, for instance, when video texture rendering (aka zero-copy optimization) is unavailable, because of HW incompatibility or when it's opt-outed via QT_DISABLE_HW_TEXTURES_CONVERSION env. variable (see https://codereview.qt-project.org/c/qt/qtmultimedia/+/504782, https://codereview.qt-project.org/c/qt/qtmultimedia/+/507785 for details).

Can be reproduced with standard Qt Quick MediaPlayer example, just open and play attached video file and observe progress bar. Make sure that you set

    QT_MEDIA_BACKEND=windows
    QT_DISABLE_HW_TEXTURES_CONVERSION=1

Reproduced with any RHI backend, such as OpenGL, D3D11, D3D11 WARP, D3D12,