follow-up to #31: handle case when source-highlighter not in use
follow-up to #31: handle case when source-highlighter not in use

- format text properly when source-highlighter is not in use
- simplify check to determine if highlighting is enabled

theimdal/asciidoctor-pdf,theimdal/asciidoctor-pdf,hmflash/asciidoctor-pdf,abatalev/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,mojavelinux/asciidoctor-pdf,Hextremist/asciidoctor-pdf,Hextremist/asciidoctor-pdf,DavidGamba/asciidoctor-pdf,hmflash/asciidoctor-pdf,DavidGamba/asciidoctor-pdf,dsisnero/asciidoctor-pdf,asciidoctor/asciidoctor-pdf,abatalev/asciidoctor-pdf,dsisnero/asciidoctor-pdf