Fix broken parser for git diffs with binaries

Review Request #10854 — Created Jan. 24, 2020 and submitted — Latest diff uploaded


Review Board


The parser for git diffs (git and hg) did a mistake
if there are base64 binary data. It prepended the data
to a following file info instead of appending the
previous one.

Uploaded the unit test diff. Downloaded the patch with
"Download Diff" and saw that it was correct. Also it
could be applied by "rbt patch".
Saw correct FileDiff entries in database as well. Before
this patch the FileDiff data was mixed data of all files.

Added a unit test and saw that it passed.