Fix regression in PCD8544.js

flip() for PCD8544 was broken by: https://github.com/SpenceKonde/EspruinoDocs/commit/0c7cd947c08e93020faae3e233d7d1bf97bb9fe3#diff-54e8aad38d317a8ea7e056d928e39c43

Turns out, it *does* need those extra two bytes at the end of each line - except on the last line, where an extra two bytes will write over the first two bytes of the first line. Weird. Now it seems to work, and the first two bytes of line 1 are okay.