handle chunks with no output; other fixups
handle chunks with no output; other fixups

jrnold/rstudio,jar1karp/rstudio,jar1karp/rstudio,jar1karp/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,JanMarvin/rstudio,jar1karp/rstudio,jar1karp/rstudio,jrnold/rstudio,jar1karp/rstudio,JanMarvin/rstudio,jar1karp/rstudio,jrnold/rstudio,jar1karp/rstudio,JanMarvin/rstudio,jrnold/rstudio,jrnold/rstudio,jrnold/rstudio,JanMarvin/rstudio,jrnold/rstudio,jrnold/rstudio,jrnold/rstudio,jar1karp/rstudio,JanMarvin/rstudio,JanMarvin/rstudio