genext2fs: fix handling of symlinks of length exactly 60

Amusingly enough, /nix/store/...-kmod-24/bin/kmod is exactly 60
characters.

pkgs/tools/filesystems/genext2fs/default.nix

@@ -8,6 +8,12 @@ stdenv.mkDerivation {
     sha256 = "1z7czvsf3ircvz2cw1cf53yifsq29ljxmj15hbgc79l6gbxbnka0";
   };
 
+  # https://sourceforge.net/p/genext2fs/bugs/2/
+  # Will be fixed in the next release, whenever this happens
+  postPatch = ''
+    sed -e 's@4 [*] (EXT2_TIND_BLOCK+1)@-1+&@' -i genext2fs.c
+  '';
+
   meta = with stdenv.lib; {
     homepage = http://genext2fs.sourceforge.net/;
     description = "A tool to generate ext2 filesystem images without requiring root privileges";