TractionLimiter: Fix wrong input checks (backport #1341)

[mergify]

While working on ros-controls/control_toolbox#212 and writing tests, I found some issues with the TractionLimiter of the tricycle_controller.

---

This is an automatic backport of pull request #1341 done by Mergify.

[codecov]

Codecov Report

Attention: Patch coverage is 57.29730% with 79 lines in your changes missing coverage. Please review.

Project coverage is 65.17%. Comparing base (af1a840) to head (f63b410).
Report is 1 commits behind head on iron.

Files with missing lines	Patch %	Lines
tricycle_controller/test/test_traction_limiter.cpp	54.33%	0 Missing and 79 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             iron    #1367      +/-   ##
==========================================
+ Coverage   64.92%   65.17%   +0.25%     
==========================================
  Files         107      108       +1     
  Lines       12283    12464     +181     
  Branches     7577     7711     +134     
==========================================
+ Hits         7975     8124     +149     
+ Misses       1540     1507      -33     
- Partials     2768     2833      +65     

Flag	Coverage Δ
unittests	65.17% <57.29%> (+0.25%)	⬆️

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

Files with missing lines	Coverage Δ
tricycle_controller/src/traction_limiter.cpp	95.77% <100.00%> (+73.55%)	⬆️
tricycle_controller/test/test_traction_limiter.cpp	54.33% <54.33%> (ø)

... and 1 file with indirect coverage changes