string: avoid undefined behavior in strrchr()

string: avoid undefined behavior in strrchr()

The pre-decrement would not only cause misbehavior when wrapping (benign
because there shouldn't be any NULL pointers passed in), but may also
create a pointer pointing outside the object that the passed in pointer
points to (it won't be de-referenced though).

Take the opportunity and also
- convert bogus space (partly 7 of them) indentation to Linux style tab
  one,
- add two blank lines.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>