File comments were causing an exception when displayed on the
change view because python3 does not allow comparing None to int,
and file comments have a line number of None.
To correct this, use 0 as the line number for file comments whin
sorting and displaying them in the change view; there is no line
0 so this minor aliasing shouldn't cause any collisions.
Also, add a newline to the end of file comments, just as regular
inline comments (otherwise if a file comment was followed by a
line comment, they would appear on the same line).
Change-Id: Iedf88cdfd83adbc405e26cb013c9f57481d50c90
0e770f0df6