fix test for sdsrange in sds.c

in sds.c

main function has invalid tests for sdsrange.

so I fixed it to be able to build.

This is not important. but it might need for consistency for usage of sdsrange

```c
1 - Create a string and obtain the length: PASSED
2 - Create a string with specified length: PASSED
3 - Strings concatenation: PASSED
4 - sdscpy() against an originally longer string: PASSED
5 - sdscpy() against an originally shorter string: PASSED
6 - sdscatprintf() seems working in the base case: PASSED
7 - sdstrim() correctly trims characters: PASSED
8 - sdsrange(...,1,1): PASSED
9 - sdsrange(...,1,-1): PASSED
10 - sdsrange(...,-2,-1): PASSED
11 - sdsrange(...,2,1): PASSED
12 - sdsrange(...,1,100): PASSED
13 - sdsrange(...,100,100): PASSED
14 - sdscmp(foo,foa): PASSED
15 - sdscmp(bar,bar): PASSED
16 - sdscmp(bar,bar): PASSED
17 - sdsnew() free/len buffers: PASSED
18 - sdsMakeRoomFor(): PASSED
19 - sdsIncrLen() -- content: PASSED
20 - sdsIncrLen() -- len: PASSED
21 - sdsIncrLen() -- free: PASSED
21 tests, 21 passed, 0 failed
```