Swap rstrip() and lskip() to reduce execution time of strlen()

[isidroas]

I confess that the optimization is minimal. But it is free because it does not complicates the code.

With this change, I measured the time spent on the first call of strlen():

$ python3 -c 'print(" "*4000 + "name=value")' > long_padding.ini
$ gcc examples/ini_dump.c ini.c -o examples/ini_dump
$ ltrace -T -e strlen ./examples/ini_dump long_padding.ini
ini_dump->strlen("name=value\n")                                     = 11 <0.000147>

and without this change (master):

ini_dump->strlen("                                "...)              = 4011 <0.001856>

The execution time was reduced from 1856 ns to 147 ns.

[benhoyt]

This makes sense to me, thanks!