This update should remove the interference between the two play buttons in exercise and MIDI player controls. And it will work on the latest one. Like if our exercise was working and now we open a .mid file, now only the MIDI player controls will work, and pressing the play exercise button won't have any effect. Similarly, if the midi file is playing and we request for a new exercise, the midi player will be turned off (timer to 0) and the exercise will play. Now the MIDI player play button won't work. Before creating a new exercise, I have stopped the midi player first and then cleared the old Song object for midi before creating a new song object.

@ahassan Dont drop diff here, create a differential at https://phabricator.kde.org/differential/diff/create/
It will make testing and reviewing easy.

@itsback Thank you for your help. I really appreciate it.