Prompted to save before closing unedited "My_First_Score"

d45cc19 Ubuntu nightly (also affects 2.0.2 and is probably OS independent).

1. Start MuseScore.
2. Close the Start Centre so you are looking at "My_First_Score".
3. Without closing MuseScore, close "My_First_Score" via its tab.

Expected behaviour: The score should close without prompting because no edits have been made.

Actual behaviour: MuseScore prompts to save the score before closing.

This is particularly annoying because "My_First_Score" opens automatically when MuseScore starts so the user probably didn't want it open in the first place.

Note: An asterisk (*) is displayed after the filename in the tab only after the score has been edited, and it disappears if the user performs "undo" operations until all changes have gone. This behaviour is normal, but it is interesting that MuseScore "knows" the file has not changed (since no asterisk is displayed) yet it still prompts to save the file.