Skip updating ignition plugins when simulation is paused

[luca-della-vedova]

Bug fix

Fixed bug

Closes rmf_demos #71.

Fix applied

Add a check in every plugin and, if the simulation is paused, skip updating.
The crash was caused by the state being updated when simulation is paused, which resulted in a value of dt of 0 being used, then divisions by 0 in the velocity calculation resulted in nan values being sent to the physics engine.

[codecov]

Codecov Report

Merging #34 (0d7bb4f) into main (a81991f) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##            main     #34      +/-   ##
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  Coverage   0.00%   0.00%              
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  Files        640      46     -594     
  Lines      54080    3752   -50328     
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+ Misses     54080    3752   -50328     

Flag	Coverage Δ
tests	0.00% <ø> (ø)

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Impacted Files	Coverage Δ
...ation/rmf_building_sim_gazebo_plugins/src/lift.cpp
...uilding_sim_gazebo_plugins/src/toggle_charging.cpp
...tion/rmf_robot_sim_gazebo_plugins/src/readonly.cpp
...ation/rmf_robot_sim_common/src/ingestor_common.cpp
...ation/rmf_robot_sim_common/src/ingestor_common.cpp
...ation/rmf_robot_sim_common/src/readonly_common.cpp
...lation/rmf_building_sim_common/src/door_common.cpp
...building_sim_common/src/crowd_simulator_common.cpp
...lation/rmf_building_sim_common/src/door_common.cpp
...lation/rmf_robot_sim_common/src/slotcar_common.cpp
... and 672 more