Fix #144254: VSE proxies for image sequences do not work

Broken with new 4.5 cache implementation; the loop for building
image sequence proxies was not flushing the intra-frame cache
between frame changes. This affects image proxies since they go
through the whole VSE render stack; does not affect video proxies
since they just manually decode the file frames.

Pull Request: https://projects.blender.org/blender/blender/pulls/144269

source/blender/sequencer/intern/proxy.cc

@@ -44,6 +44,7 @@
 #include "SEQ_sequencer.hh"
 #include "SEQ_time.hh"
 
+#include "cache/intra_frame_cache.hh"
 #include "multiview.hh"
 #include "proxy.hh"
 #include "render.hh"
@@ -563,6 +564,12 @@ void proxy_rebuild(IndexBuildContext *context, wmJobWorkerStatus *worker_status)
        timeline_frame < time_right_handle_frame_get(scene, strip);
        timeline_frame++)
   {
+    intra_frame_cache_set_cur_frame(render_context.scene,
+                                    timeline_frame,
+                                    render_context.view_id,
+                                    render_context.rectx,
+                                    render_context.recty);
+
     if (context->size_flags & IMB_PROXY_25) {
       seq_proxy_build_frame(&render_context, &state, strip, timeline_frame, 25, overwrite);
     }