Disallow creating comments on line 0

Users were able to create comments on line 0 by clicking on the
missing side of a hunk and creating a comment there.  This was not
something we expected users to do, resulting in a saved draft which
cannot be displayed as we never draw line 0 of a file.

Bug: GERRIT-262
Change-Id: I3e09bada23be68f417a949b5b6969c8c75523ca5
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed