Windows QPA: Call InvalidateRect() in WM_PAINT/GL Software rendering

Bring back the call to InvalidateRect() removed by change
6086c81e4d since it seems that GL Software rendering
requires it (also for single buffer mode).

Task-number: QTBUG-58178
Change-Id: I197a1b3c3906c4afa43943db30dbc07dfb656cc7
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -43,7 +43,7 @@
 #include "qwindowsscreen.h"
 #include "qwindowsintegration.h"
 #include "qwindowsnativeinterface.h"
-#include "qwindowsopenglcontext.h"
+#include "qwindowsglcontext.h"
 #ifdef QT_NO_CURSOR
 #  include "qwindowscursor.h"
 #endif
@@ -1582,6 +1582,16 @@ bool QWindowsWindow::handleWmPaint(HWND hwnd, UINT message,
         return false;
     PAINTSTRUCT ps;
 
+#if QT_CONFIG(dynamicgl)
+    // QTBUG-58178: GL software rendering needs InvalidateRect() to suppress
+    // artifacts while resizing.
+    if (testFlag(OpenGLSurface)
+        && QOpenGLStaticContext::opengl32.moduleIsNotOpengl32()
+        && QOpenGLContext::openGLModuleType() == QOpenGLContext::LibGL) {
+        InvalidateRect(hwnd, 0, false);
+    }
+#endif // dynamicgl
+
     BeginPaint(hwnd, &ps);
 
     // Observed painting problems with Aero style disabled (QTBUG-7865).