sim_main: Print clear error in case CreateProcessA fails (backport #3104)

[mergify]

🦟 Bug fix

Summary

Without this fix, if for any reason the invocation of the gz-sim-gui-client fails on Windows, the gz-sim-main process (or the parent process gz) silently exits, that may be confusing for users.

See conda-forge/gz-sim-feedstock#110 .

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)
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This is an automatic backport of pull request #3104 done by [Mergify](https://mergify.com).