Stop the render loop before emptying the singleton window for reuse

Reverts effects of previous commit since that caused an accumulation
of screens after each save, which balooned memory requirements.
Instead, just copy the one line from `close()` which has an effect
other than manipulating the window visibility state.

GLMakie/src/screen.jl

@@ -322,6 +322,7 @@ function singleton_screen(debugging::Bool)
     if !isempty(SINGLETON_SCREEN)
         @debug("reusing singleton screen")
         screen = SINGLETON_SCREEN[1]
+        stop_renderloop!(screen; close_after_renderloop=false)
         empty!(screen)
     else
         @debug("new singleton screen")
@@ -428,7 +429,7 @@ end
 
 # Screen to save a png/jpeg to file or io
 function Screen(scene::Scene, config::ScreenConfig, io::Union{Nothing, String, IO}, typ::MIME; visible=nothing, start_renderloop=false)
-    screen = screen_from_pool(config.debugging)
+    screen = singleton_screen(config.debugging)
     !isnothing(visible) && (config.visible = visible)
     apply_config!(screen, config; start_renderloop=start_renderloop)
     display_scene!(screen, scene)
@@ -437,7 +438,7 @@ end
 
 # Screen that is efficient for `colorbuffer(screen)`
 function Screen(scene::Scene, config::ScreenConfig, ::Makie.ImageStorageFormat;  start_renderloop=false)
-    screen = screen_from_pool(config.debugging)
+    screen = singleton_screen(config.debugging)
     config.visible = false
     apply_config!(screen, config; start_renderloop=start_renderloop)
     display_scene!(screen, scene)