Update GUI Runner initial state request timing (backport #3044)

[mergify]

🦟 Bug fix

Related issue: gazebosim/jetty_demo#3

Summary

While testing the Jetty demo world, it was found that Gazebo took a while to load because there is a large number of entities in the world. The slow down is mainly on the GUI side. One cause of the long load time was found to be that the GuiRunner setting its ECM initial state twice: Once from the async state request and the other from the state topic subscription callback (sync version).

More info:

There was a PR (#1073) to only start the processing the states from topic subscription callback (sync version) only after the async version is done, which is tracked using the this->dataPtr->receivedInitialState bool variable. That worked fine until this merge forward change that changed the processing of the state request in the aysnc callback to a QueuedConnection. As the result, the state is not processed immediately but this->dataPtr->receivedInitialState is incorrectly marked as true. This causes the sync version to start processing states right away.

The fix is to properly set this->dataPtr->receivedInitialState to true in the state callback function after the states are actually processed.

This patch reduces the load time by ~15 seconds (from ~1min 10sec to ~55 sec) on my machine.

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)
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This is an automatic backport of pull request #3044 done by [Mergify](https://mergify.com).

[mergify]

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