[LyX/2.3.x] Backport getContentsMargins() deprecation fix

[Juergen Spitzmueller]

commit 9671f8ca2023c43e49baa69be61b1bb4ccdcb227
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Mar 13 12:21:50 2021 +0100

    Backport getContentsMargins() deprecation fix
---
 src/frontends/qt4/GuiView.cpp |    3 +--
 1 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt4/GuiView.cpp b/src/frontends/qt4/GuiView.cpp
index 8d73c02..60e59ef 100644
--- a/src/frontends/qt4/GuiView.cpp
+++ b/src/frontends/qt4/GuiView.cpp
@@ -4390,8 +4390,7 @@ bool GuiView::lfunUiToggle(string const & ui_component)
 		menuBar()->setVisible(!menuBar()->isVisible());
 	} else
 	if (ui_component == "frame") {
-		int l, t, r, b;
-		getContentsMargins(&l, &t, &r, &b);
+		int const l = contentsMargins().left();
 		//are the frames in default state?
 		d.current_work_area_->setFrameStyle(QFrame::NoFrame);
 		if (l == 0) {