Fix locks in Visualize Lidar GUI plugin

[iche033]

🦟 Bug fix

Fixes #1487

Summary

I ran into segfaults using the Visualize Lidar GUI plugin before. It happens when closing the plugin for me. A crash that could be related to this was reported downstream in osrf/mbzirc#150. This PR fixes obvious locking syntax errors in Visualize Lidar GUI plugin. I also removed the one in OnRefresh as that causes a deadlock.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[codecov]

Codecov Report

Merging #1538 (70ffa2e) into ign-gazebo6 (b753afe) will increase coverage by 2.50%.
The diff coverage is n/a.

@@               Coverage Diff               @@
##           ign-gazebo6    #1538      +/-   ##
===============================================
+ Coverage        61.52%   64.03%   +2.50%     
===============================================
  Files              361      316      -45     
  Lines            27733    25462    -2271     
===============================================
- Hits             17063    16304     -759     
+ Misses           10670     9158    -1512     

Impacted Files	Coverage Δ
src/gui/plugins/entity_tree/moc_EntityTree.cpp
src/gui/plugins/plot_3d/moc_Plot3D.cpp
src/msgs/peer_info.pb.h
...c/gui/plugins/scene_manager/moc_GzSceneManager.cpp
..._/__/include/ignition/gazebo/gui/moc_GuiSystem.cpp
src/gui/plugins/copy_paste/moc_CopyPaste.cpp
src/gui/plugins/entity_tree/qrc_EntityTree.cpp
src/gui/plugins/lights/moc_Lights.cpp
...gui/plugins/select_entities/moc_SelectEntities.cpp
src/gui/plugins/spawn/qrc_Spawn.cpp
... and 35 more

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[mjcarroll]

LGTM. That's a pretty subtle error, those locks weren't doing anything.

Might be worthwhile to do a search to make sure we aren't doing that anywhere else.

[iche033]

Might be worthwhile to do a search to make sure we aren't doing that anywhere else.

just did a grep for "std::mutex>(" and "std::recursive_mutex>(" and only found ones in VisualizeLidar. I think we're safe for now.