"complete.txt" gets written even if interrupted

During a test, I downloaded a comic but hit ctrl-c partway through.  It said "WARNING: Interrupted! Waiting for download threads to finish.", then exited.  However, a subsequent run said "All comics are already downloaded.".  I needed to first delete `complete.txt` before it would check the pages and resume downloading.  Ideally, on interrupt it would not write complete.txt.