#388 Arithmetic expetion in update_shrink_ranges()

[Frank Markesteijn]

When for some reason the height and width of the cropped area of an image are zero a division by zero occurs in update_shrink_ranges() in ufraw_preview.c at line 1990. You can fix this by inserting this at line 1984:
if (size == 0 || (croppedHeight == 0 && croppedWidth == 0))
data->height = data->width = data->shrink = 0;
else