File gr-display-use-nullptr.patch of Package gr-display

diff -up gr-display/lib/showpngpicture.cc.aaaa gr-display/lib/showpngpicture.cc
--- gr-display/lib/showpngpicture.cc.aaaa	2021-06-27 01:50:40.473491459 +0200
+++ gr-display/lib/showpngpicture.cc	2021-06-27 01:51:18.434521809 +0200
@@ -97,7 +97,7 @@ void  ShowPngPicture::setNextPixel(int i
 void ShowPngPicture::paintEvent(QPaintEvent *)
 {
 
-  if(p > 0)
+  if(p != nullptr)
     ui->displayWidget->setPixmap(QPixmap::fromImage(*p));
 }
 bool ShowPngPicture::saveImage(QString datei)