Fix null handling in ls_sort
Fix null handling in ls_sort

radare/sdb,radare/sdb,radare/sdb,alvarofe/sdb,radare/sdb,radare/sdb,radare/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,radare/sdb,radare/sdb,radare/sdb,alvarofe/sdb,alvarofe/sdb,alvarofe/sdb,radare/sdb,radare/sdb