[LyX/2.3.x] Backport QMatrix deprecation fixes

[Juergen Spitzmueller]

commit 75095fdc6e7f288e9dfb542da8d5acf768d7aea4
Author: Juergen Spitzmueller <spitz at lyx.org>
Date:   Sat Mar 13 12:06:06 2021 +0100

    Backport QMatrix deprecation fixes
---
 src/frontends/qt4/GuiImage.cpp |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/frontends/qt4/GuiImage.cpp b/src/frontends/qt4/GuiImage.cpp
index c73fe7c..5f398b1 100644
--- a/src/frontends/qt4/GuiImage.cpp
+++ b/src/frontends/qt4/GuiImage.cpp
@@ -177,7 +177,7 @@ bool GuiImage::rotate(Params const & params)
 		return false;
 
 	QImage const & image = is_transformed_ ? transformed_ : original_;
-	QMatrix m;
+	QTransform m;
 	m.rotate(- params.angle);
 	transformed_ = image.transformed(m);
 	return true;
@@ -205,7 +205,7 @@ bool GuiImage::scale(Params const & params)
 	scale += 0.0001;
 #endif
 
-	QMatrix m;
+	QTransform m;
 	m.scale(scale, scale);
 	// Bilinear filtering is used to scale graphics preview
 	transformed_ = image.transformed(m, Qt::SmoothTransformation);