Fully hide song editor scrollbar when not needed

[Spekular]

Previously, the scrollbar's background area would still be displayed.
To work around this, resize the scrollbar area to 0px when it's not needed.

[BaraMGB]

I found a simpler solution:

lmms/src/gui/TrackContainerView.cpp

Line 491 in 1c715bc

setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOn );

becomes to:
setVerticalScrollBarPolicy( Qt::ScrollBarAsNeeded );
and:

lmms/src/gui/TrackContainerView.cpp

Lines 230 to 231 in 1c715bc

	content->setFixedWidth( width()
	- m_scrollArea->verticalScrollBar()->width() );

becomes to:
content->setFixedWidth(width());

[Spekular]

setVerticalScrollBarPolicy is set to ScrollBarAsNeeded by default, and I saw no difference by calling m_scrollArea->setVerticalScrollBarPolicy( Qt::ScrollBarAsNeeded ) in TrackContainerView::TrackContainerView. But if your version works then that is indeed a whole lot simpler. I guess you tested it @BaraMGB ?

[BaraMGB]

Sorry I reformated the comment above.

[BaraMGB]

Yes I've tested it.

[Spekular]

Also, I believe there will be a slight visual difference between my solution and always having the full width. The timeline drew above (vertically, not depthwise) the scrollbar when I did that. It doesn't look very buggy though so I suppose that behavior is fine.

Got a build running to test it, no difference.

[BaraMGB]

It looks exactly the same.

[Spekular]

It does indeed.

[Spekular]

@BaraMGB You may as well commit this yourself, if you don't mind. You can remove this line entirely instead of explicitly setting it to AsNeeded, I just tested:

lmms/src/gui/TrackContainerView.cpp

Line 491 in 1c715bc

setVerticalScrollBarPolicy( Qt::ScrollBarAlwaysOn );