Speculative workaround for QWidgetPrivate::subtractOpaqueSiblings crash

qrenderdoc/Code/qrenderdoc.cpp

@@ -86,6 +86,11 @@ int main(int argc, char *argv[])
 
   qInstallMessageHandler(sharedLogOutput);
 
+  // there seems to be a persistent crash in QWidgetPrivate::subtractOpaqueSiblings where a widget
+  // has no parent but is not a window. Try to work around it by setting this env var, as it's only
+  // an optimisation
+  qputenv("QT_NO_SUBTRACTOPAQUESIBLINGS", lit("1").toUtf8());
+
   qInfo() << "QRenderDoc initialising.";
 
   if(IsRunningAsAdmin())