Remove spurious whitespace from blank lines in diff views

We shouldn't put an   entity into the line if the line is empty,
as it shows a space when the user tries to select the line text.  In
theory I had put these here to preserve the line height, but that is
already taken care of for us by the line numbers which appear in the
same table row, using the same font.

Bug: GERRIT-211
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed