[ptx] nona output file dimensions

[Tim Jacobs]

I'm using nona with the following script. The output file size is
w2048 by h1535 (i.e. the height is short by 1 pixel). If I change to
h1537, I get an image 1537 pixels high. Any insight as to what's going
on?

p w2048 h1536 f0 v40.83492 n"JPEG g0 q90 "
m g1 i0
o w2048 h1536 f0 y0 r0 p0 v40.83492 a0.007043 b-0.024821 c0.000000 d0
e0 n"test.jpg"

Thanks,
Tim