Fix render rate.

Depending on how the threads get assigned, the actual render rate (not just the stats) could be as little as a third of what is targetted.

That's because the code was insisting on an empty texture escrow before our update/render cycle could begin, and otherwise just waits for the next whole cycle.
On my MacbookPro, this was regularly giving a render average of 20fps instead of 60.

libraries/display-plugins/src/display-plugins/OpenGLDisplayPlugin.cpp

@@ -157,7 +157,7 @@ OpenGLDisplayPlugin::OpenGLDisplayPlugin() {
     });
 
     connect(&_timer, &QTimer::timeout, this, [&] {
-        if (_active && _sceneTextureEscrow.depth() < 1) {
+        if (_active && _sceneTextureEscrow.depth() <= 1) {
             emit requestRender();
         }
     });