Fix build with Qt 5.15

Authored-by: Thomas Posch <bugs.gentoo.org@online.posch.name>

diff -Naur a/core/dplugins/generic/view/presentation/opengl/presentationgl.cpp b/core/dplugins/generic/view/presentation/opengl/presentationgl.cpp
--- a/core/dplugins/generic/view/presentation/opengl/presentationgl.cpp	2020-06-30 22:48:50.477149053 +0200
+++ b/core/dplugins/generic/view/presentation/opengl/presentationgl.cpp	2020-06-30 22:49:52.217439213 +0200
@@ -44,6 +44,8 @@
 #include <QMatrix>
 #include <QMouseEvent>
 #include <QPainter>
+#include <QPainterPath>
+#include <QPainterPathStroker>
 #include <QPixmap>
 #include <QTimer>
 #include <QWheelEvent>
diff -Naur a/core/libs/dimg/filters/curves/curveswidget.cpp b/core/libs/dimg/filters/curves/curveswidget.cpp
--- a/core/libs/dimg/filters/curves/curveswidget.cpp	2020-06-30 22:48:50.374150231 +0200
+++ b/core/libs/dimg/filters/curves/curveswidget.cpp	2020-06-30 22:49:17.219842551 +0200
@@ -41,6 +41,7 @@
 #include <QFont>
 #include <QFontMetrics>
 #include <QPaintEvent>
+#include <QPainterPath>
 #include <QMouseEvent>
 
 // KDE includes
diff -Naur a/core/libs/dimg/filters/levels/histogrampainter.cpp b/core/libs/dimg/filters/levels/histogrampainter.cpp
--- a/core/libs/dimg/filters/levels/histogrampainter.cpp	2020-06-30 22:48:50.374150231 +0200
+++ b/core/libs/dimg/filters/levels/histogrampainter.cpp	2020-06-30 22:49:17.219842551 +0200
@@ -30,6 +30,7 @@
 // Qt includes
 
 #include <QPainter>
+#include <QPainterPath>
 
 // KDE includes
 
