hwdec-current property does not get updated when changing hwdec #4289

mpv version and platform

• Both 0.24 and master (c68be80a63f100d1a55d8be7273c89734d6abeeb)
• macOS Sierra 10.12.4

Reproduction steps

Using the client API:

• observe hwdec-current
• init mpv with --opengl-hwdec-interop=auto and--hwdec=auto
• play a video
• I do get hwdec-current changed to videotoolbox-copy when playback starts
• a few seconds later, set --hwdec=no (can confirm it switched back to software decoding)

Expected behavior

Receive a change in hwdec-current (should become no)

Actual behavior

Not receiving any changes for hwdec-current.

Also, after doing --hwdec=no, switching back to --hwdec=auto again does switch back to videotoolbox (can confirm hardware decoding), but hwdec-current never changes.