* asciitopgm: fix bug: memory corruption on too-long lines.
* asciitopgm: fix bug: improper handling of blank lines.
* pngtopnm: fix bug: -verbose reports history chunk present when
it's really a palette.
* bmptopnm: Don't crash on invalid zero value of image height in
the BMP header of a compressed file.
* bmptopnm: don't crash on large invalid value of 'colorsused' in
the BMP header.
* ilbmtoppm: Don't crash on image that has a transparent color
index, but no color map.
OBS-URL: https://build.opensuse.org/package/show/graphics/netpbm?expand=0&rev=29
