[patch] citeproc-js 1.0.52 compatibility patch

[fbennett]

With the processor now being good about quashing duplicate spaces, there is a problem with space-terminated RTF control characters. This patch accomodates the replacement of terminal control words ending in a space, like "\i0 " and "\supersub ", with versions ending at an empty group, like "\i0{}" and "\supersub{}".

The patch is specific to processor version 1.0.52 and above, and should be applied together with that version of the processor.