-n to index from end is broken

[yigitsever]

Hello,

Using negative indices to index from the end is broken with commit a4c5de9, tested and verified with git bisect:

Current behaviour:

$ buku -p -1                                                                                                      
[ERROR] No matching index [-1]

Expected behaviour:

$ buku -p -1 
1542. GitHub - jarun/buku: :bookmark: Personal mini-web in text
   > https://github.com/jarun/buku/
   + :bookmark: Personal mini-web in text. Contribute to jarun/buku development by creating an account on GitHub.
   # tool

[jarun]

@LeXofLeviafan please have a look.