Fix T65333: VSE: Playback speed regression

3D engine settings were used to select image scaling method.
Use higher quality scaling only for rendering.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D4995

source/blender/blenkernel/intern/sequencer.c

@@ -2787,7 +2787,7 @@ static ImBuf *input_preprocess(const SeqRenderData *context,
   }
 
   if (ibuf->x != context->rectx || ibuf->y != context->recty) {
-    if (scene->display.render_aa > SCE_DISPLAY_AA_FXAA) {
+    if (context->for_render) {
       IMB_scaleImBuf(ibuf, (short)context->rectx, (short)context->recty);
     }
     else {