Fix mpv pause state when loading new media

- Bugfix for volume setting
- Making duck() unduck() stable

tests/test_libmpv_player.py

@@ -17,6 +17,22 @@ time.sleep(2)
 player.resume()
 time.sleep(5)
 
+print("Set volume to 80")
+player.set_volume(80)
+time.sleep(2)
+
+print("Duck")
+player.duck()
+time.sleep(2)
+
+print("Set volume to 40 while ducked")
+player.set_volume(40)
+time.sleep(2)
+
+print("Unduck")
+player.unduck()
+time.sleep(2)
+
 player.stop()
 time.sleep(2)