MAC/do: parse_rules(): Copy input string on its own

[olce]

Summary

This revision is part of a series. Click on the Stack tab below to see the context.
This series has also been squeezed into D47633 to provide an overall view.

Commit message:
Since all callers have to do it, save them that burden and do it in
parse_rules() instead.

While here, replace 'strlen(x) == 0' with the simpler and more efficient
'x[0] == 0'.

[lwhsu]

In the proposed commit message, I guess you mean:

While here, replace strlen(x) == 0 with the simpler and more efficient
x[0] == '\0'.

Note 0 and \0. I believe the later is better.

[olce]

In D47591#1086749, @lwhsu wrote:

Note 0 and \0. I believe the later is better.

Yes. The initial version probably was using 0 and later I changed the code but forgetting to update the commit message. Will do.