vcomp/jpegxs: when send fail, release the buffer

The error triggered <https://github.com/CESNET/UltraGrid/issues/492>
causes freeze on svt_jpeg_xs_frame_pool_get().

It doesn't work, anyways - perhaps incorrect handling in SVT-JPEG-XS. At least
when `enc_input.image.ready_to_release` is not set to 1, current impl of
svt_jpeg_xs_frame_pool_release() doesn't release anything. But even if
set to 1, it still doesn't help.

So at least fixing our use and hopefully it will get also fixed
upstram. This shouldn't happen, anyways, unless passwdd wrong parameters
as in the #492.

src/video_compress/jpegxs.cpp

@@ -210,6 +210,8 @@ static void jpegxs_worker_send(state_video_compress_jpegxs *s) {
                 err = svt_jpeg_xs_encoder_send_picture(&s->encoder, &enc_input, /*blocking*/ 1);
                 if (err != SvtJxsErrorNone) {
                         print_svt_jxs_error(err, "Failed to send frame to encoder");
+                        free(enc_input.user_prv_ctx_ptr);
+                        svt_jpeg_xs_frame_pool_release(s->frame_pool, &enc_input);
                         continue;
                 }