- Fix conditional buildreq for Leap 15.x & co

- Update to 7.28
This fixes a couple of major regressions in the previous version:
* Fixed seeking and frozen video due by reverting “Improved
performance with intra-only video and reducing the frame
rate.”
* Fixed using melt to render MLT XML with OpenGL effects from
movit.
Other fixes and changes:
* Deprecated the composite transition and the sdl and ndi
modules.
* Fixed Android camera video has the wrong frame rate (broken
in v7.26.0).
* Fixed audio not playing for audio-only DTS WMA.
* Fixed using “https:” URLs in the xml producer.
* Fixed crash on exit when running melt -query or melt -query
links.
* Added a transition property to the watermark filter. Now, it
defaults to using affine.
* Changed affine transition argument to set rect property if
supplied.