Command final waypoint identically when traj_point_active_ptr_ is null

[egordon]

Addresses #671

Redux of #672 fix sent directly to master.
Requesting a back-port to humble if possible, as this seems to fix a bug noticed by anybody using closed-loop velocity or effort hardware control.

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[codecov-commenter]

Codecov Report

Merging #682 (6919f38) into master (e7f9962) will increase coverage by 0.75%.
The diff coverage is 34.91%.

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@@            Coverage Diff             @@
##           master     #682      +/-   ##
==========================================
+ Coverage   35.78%   36.53%   +0.75%     
==========================================
  Files         189        7     -182     
  Lines       17570      676   -16894     
  Branches    11592      357   -11235     
==========================================
- Hits         6287      247    -6040     
+ Misses        994      134     -860     
+ Partials    10289      295    -9994     

Flag	Coverage Δ
unittests	36.53% <34.91%> (+0.75%)	⬆️

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

Impacted Files	Coverage Δ
...ontroller/test/test_load_diff_drive_controller.cpp	11.11% <0.00%> (ø)
diff_drive_controller/src/odometry.cpp	42.16% <11.11%> (ø)
diff_drive_controller/src/speed_limiter.cpp	46.55% <11.11%> (ø)
...ive_controller/test/test_diff_drive_controller.cpp	17.62% <12.08%> (ø)
...iff_drive_controller/src/diff_drive_controller.cpp	47.09% <46.88%> (ø)
...de/diff_drive_controller/diff_drive_controller.hpp	100.00% <100.00%> (ø)
...troller/include/diff_drive_controller/odometry.hpp	100.00% <100.00%> (ø)

... and 189 files with indirect coverage changes