Fix extra end of phrase after the last note

[Tuupertunut]

What does this PR do?

Fixes the issue where the editor saved song files with an additional end-of-phrase marker after the last note, as described in #573.

Closes Issue(s)

#573

Additional Notes

There is a wiki page with an example song file with extra end-of-phrase markers that needs to be updated if this gets merged.
https://github.com/UltraStar-Deluxe/Play/wiki/UltraStar-txt-File-Format

[achimmihca]

I would prefer setting the flag based on "is this the last sentence".
Consider to iterate by index, then check if index matches (sentences length - 1).

[Tuupertunut]

Do you mean something like

for all sentences
{
    AppendSentence(... , (i == last))
}

[Tuupertunut]

I refactored that loop to check index.

[achimmihca]

Please add a Edit Mode test for this. See Assets/Editor/Tests.
The Edit Mode tests are simple unit tests, much simplier than the Play Mode test.

[achimmihca]

There is a wiki page with an example song file with extra end-of-phrase markers that needs to be updated if this gets merged.

I sent you an invitation to the repo with WRITE access. You should now be able to edit the wiki pages.
Can edit the wiki in browser, or via its repo: https://github.com/UltraStar-Deluxe/Play.wiki.git

[Tuupertunut]

I added an edit mode test for this fix.