Yikes! Nice catch and a huge thanks for providing a reproducible example -- I can indeed confirm that attempting to execute a chunk that contains an incomplete chunk header causes an RStudio crash (usually on the second attempt to execute the chunk, at least in my case).
@atiretoo We've got a preview up this morning, 1.1.379, that contains a fix for this issue. Give it a try if you have time and let us know if addresses the problem for you!