qpa: Set minimum device ratio of 1 for windows

This is to prevent rendering issues in the present windows close buttons
as Qt supports scale factors that are less than one poorly.

src/plugins/qpa/window.cpp

@@ -29,7 +29,7 @@ Window::Window(QWindow *window)
     : QPlatformWindow(window)
     , m_eglDisplay(kwinApp()->platform()->sceneEglDisplay())
     , m_windowId(++s_windowId)
-    , m_scale(screens()->maxScale())
+    , m_scale(std::max(qreal(1), screens()->maxScale()))
 {
     if (window->surfaceType() == QSurface::OpenGLSurface) {
         // The window will use OpenGL for drawing.

src/plugins/qpa/window.h

@@ -57,7 +57,7 @@ private:
     EGLSurface m_eglSurface = EGL_NO_SURFACE;
     quint32 m_windowId;
     bool m_resized = false;
-    int m_scale = 1;
+    qreal m_scale = 1;
 };
 
 }