Switch back to "live" renders when doing preview renders to Blender's…

… render view window.

We need to be able to get pixels from the display driver, at the end of render. Unfortunately, by the time
we request the last of the pixels, the renderer might have already shut down the display driver.
This change means we cannot
do non-incremental renders when rendering to Blender, unfortunately.

rman_render.py

@@ -523,6 +523,8 @@ def start_render(self, depsgraph, for_background=False):
             return False            
 
         render_cmd = "prman"
+        if self.rman_render_into == 'blender':
+            render_cmd = "prman -live"
         render_cmd = self._append_render_cmd(render_cmd)
         self.sg_scene.Render(render_cmd)
         if self.rman_render_into == 'blender':