Ignore diff results which aren't actually hunks.

Some people have reported a failure whereby at least one `line` in the
diff results doesn't match the hunk regexp.  I believe, though cannot
say with certainty, that this is due to mismatching newline shenanigans.

However this theory doesn't explain how the failure could occur on a
file without changes, as reported by one person.  Furthermore I think
that the hunk results would have to have double \n characters to cause
this failure, which I don't think would ordinarily occur on Windows or
Unix.

Whatever the reason, this change copes with the situation.