Extends PR #4236 to cover 1-instruction blocks in filtered traces, and not just 0-instruction blocks, using the top-level filter type flag. This avoids filling the buffer up with markers using the escape back to the main loop from PR #4236.
Tested on a proprietary app where drcachesim with filtering hits the assert added in PR #4236. This change fixes it.
For a local test: it may be tricky to arrange a live trace to have enough markers in a row; maybe a synthetic trace. For now just going with the manual proprietary test run.
Issue: #4159