Fix - MacOS - get currentScreen on the edge bottom and right returns nullptr and application crashes

(cherry picked from commit 01ae74fbed34849db485db53ffbdf4a938ebea8e)

src/core/qguiappcurrentscreen.cpp

@@ -0,0 +1,65 @@
+//
+// Created by yuriypuchkov on 09.02.2021.
+//
+
+#include "qguiappcurrentscreen.h"
+#include <QCursor>
+#include <QDesktopWidget>
+#include <QGuiApplication>
+#include <QPoint>
+#include <QScreen>
+
+QGuiAppCurrentScreen::QGuiAppCurrentScreen()
+{
+    m_currentScreen = nullptr;
+}
+
+QScreen* QGuiAppCurrentScreen::currentScreen()
+{
+    return currentScreen(QCursor::pos());
+}
+
+QScreen* QGuiAppCurrentScreen::currentScreen(const QPoint& pos)
+{
+    m_currentScreen = screenAt(pos);
+#if (defined(Q_OS_MAC) || defined(Q_OS_MAC64) || defined(Q_OS_MACOS) ||        \
+     defined(Q_OS_MACX))
+    // On the MacOS if mouse position is at the edge of bottom or right sides
+    // qGuiApp->screenAt will return nullptr, so we need to try to find current
+    // screen by moving 1 pixel inside to the current desktop area
+    if (!m_currentScreen && pos.x() > 0) {
+        QPoint posCorrected(pos.x() - 1, pos.y());
+        m_currentScreen = screenAt(posCorrected);
+    }
+    if (!m_currentScreen && pos.y() > 0) {
+        QPoint posCorrected(pos.x(), pos.y() - 1);
+        m_currentScreen = screenAt(posCorrected);
+    }
+    if (!m_currentScreen && pos.x() > 0 && pos.y() > 0) {
+        QPoint posCorrected(pos.x() - 1, pos.y() - 1);
+        m_currentScreen = screenAt(posCorrected);
+    }
+#endif
+    if (!m_currentScreen) {
+        qCritical("Unable to get current screen, starting to use primary "
+                  "screen. It may be a cause of logical error and working with "
+                  "a wrong screen.");
+        m_currentScreen = qGuiApp->primaryScreen();
+    }
+    return m_currentScreen;
+}
+
+QScreen* QGuiAppCurrentScreen::screenAt(const QPoint& pos)
+{
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 10, 0))
+    m_currentScreen = qGuiApp->screenAt(pos);
+#else
+    for (QScreen* const screen : QGuiApplication::screens()) {
+        m_currentScreen = screen;
+        if (screen->geometry().contains(pos)) {
+            break;
+        }
+    }
+#endif
+    return m_currentScreen;
+}