Fixed ScoreView searchPage function.

As it is right now, when writing pN (N being a number) in the GoTo dialog, it would take you to page p(N+1). With  his fix the number inserted in the GoTo dialog will take you to the right page, as numbered below the workspace.

Note: I tried to make a pull request for the last commit only. I'm a bit new to working on large projects on GitHub. I've followed the git workflow from MuseScore.org. If I've done something wrong please let me know. Thank you! :)