Use cache only in current scene

Disable cache use, when rendering another scene seqbase.
Now cache limit applies only to one scene, so it can be overshot.
Cache of other scenes can be filled manually still.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D4757

source/blender/blenkernel/intern/sequencer.c

@@ -3720,6 +3720,7 @@ static ImBuf *do_render_strip_uncached(const SeqRenderData *context,
            */
           SeqRenderData local_context = *context;
           local_context.scene = seq->scene;
+          local_context.skip_cache = true;
 
           ibuf = do_render_strip_seqbase(&local_context, state, seq, nr, use_preprocess);