flats: fix two dark pixels on CRATOP1
flats: fix two dark pixels on CRATOP1

Sodaholic writes:
>CRATOP1 - Fixed two stray dark pixels in the corner, tiling will be far
>less noticeable now.

DW: http://www.doomworld.com/vb/post/1066669
Signed-off-by: RjY <83893d85028dba5ed7fb8142c08f77f1480bf584@users.sourceforge.net>

CWolfRU/freedoom,jmtd/freedoom,jmtd/freedoom,CWolfRU/freedoom,jmtd/freedoom