- remove some unnecessary casts and braces;

- add braces around a nested 'if'
- use S_OR and '?' to remove some duplicated function calls;
- replace nested 'if' with &&
- move out a common term in a sequence of 'if'
- add a comment on a potentially dangerous string manipulation



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@20196 65c4cc65-6c06-0410-ace0-fbb531ad65f3