Lua 5.1.3 bug in string.byte

[Mike Pall <mikelu-0806@...>]

The range check logic in string.byte is broken:

$ lua -e 'for i=5,-10,-1 do print(i, string.byte("abc", i)) end'
5
4
3       99
2       98
1       97
0
-1      99
-2      98
-3      97
-4
-5      97      98      99  <--- Unexpected results for -#str-2 and lower
-6      97      98
-7      97
-8
-9      97      98      99
-10     97      98      99

--Mike