siptrace: safety check for tm callback parameter

[ionutionita92]

Pre-Submission Checklist

• Commit message has the format required by CONTRIBUTING guide
• Commits are split per component (core, individual modules, libs, utils, ...)
• Each component has a single commit (if not, squash them into one commit)
• No commits to README files for modules (changes must be done to docbook files
  in doc/ subfolder, the README file is autogenerated)

Type Of Change

• Small bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds new functionality)
• Breaking change (fix or feature that would change existing functionality)

Checklist:

• PR should be backported to stable branches
• Tested changes locally
• Related to issue #XXXX (replace XXXX with an open issue number)

Description

Fix coverity found issue. Unlikely to happen but still it was a bug leading to potential crashes.

[miconda]

The commit message should explain what is fixed, not what tool reported the issue. So it should be something like:

siptrace: safety check for tm callback parameter

Also, the comments should not be related to discovery tool -- better do not add comments that are not relevant for understanding the code.

[ionutionita92]

Fixed. Sorry for not complying to the rules. Won't happen again

[miconda]

We try to be consistent and coherent with the commit messages, that's why we point them in pull request and try to have most of them relevant for the history of development.

But if it happens again, no big worries, the message in the commit of the pull request can be changed easier than after commit is merged in master.

I am going to merge it, thanks!