Fix calculation of tracking time constant (backport #511)

[mergify]

Fix a couple of issues with tracking time constant used for back propagation anti-windup strategy

• fix divide-by-zero bug in calculation of tracking time constant which cause time constant to be infinite and thus fail validation check and prevent updating of gains

Note: maybe there is a better way of fixing this but this resolved my issue where I was unable to change gains using rqt when i-gain was set to zero and tracking time constant was at its default of zero.

---

This is an automatic backport of pull request #511 done by Mergify.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (kilted@69bab29). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
control_toolbox/src/pid.cpp	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             kilted     #525   +/-   ##
=========================================
  Coverage          ?   82.61%           
=========================================
  Files             ?       29           
  Lines             ?     1985           
  Branches          ?      113           
=========================================
  Hits              ?     1640           
  Misses            ?      276           
  Partials          ?       69           

Flag	Coverage Δ
unittests	82.61% <75.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
control_toolbox/src/pid.cpp	82.53% <75.00%> (ø)

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.