Fix issue with sending line contents multiple times

Created by: camdencheek

This fixes an issue with skipping some results because the result size was too large. Basically, when translating from zoekt results to chunk matches, we were creating one chunk per line fragment rather than one chunk per line, so we were duplicating the line content.

Test plan

This search didn't work before, now it does:

Given that this code will likely not exist soon (zoekt will support chunk matches), I'm going to skip spending time writing tests for this. I will test the more stable code thoroughly