Coverity: RESOURCE_LEAK

[jmarrero]

Describe the bug

RESOURCE_LEAK found by Coverity downstream.

1. Defect type: RESOURCE_LEAK
5. rpm-ostree-2024.7/src/app/rpmostree-compose-builtin-tree.cxx:1382:7: open_arg: "glnx_mkdtempat" opens handle stored into "workdir_tmp.fd".
12. rpm-ostree-2024.7/src/app/rpmostree-compose-builtin-tree.cxx:1401:3: leaked_handle: Variable "workdir_tmp" going out of scope leaks handle "workdir_tmp.fd".
#  1399|                                           error))
#  1400|       return FALSE;
#  1401|->   return TRUE;
#  1402|   }
#  1403|   

2. Defect type: RESOURCE_LEAK
5. rpm-ostree-2024.7/src/app/rpmostree-compose-builtin-tree.cxx:1382:7: open_arg: "glnx_mkdtempat" opens handle stored into "workdir_tmp.fd".
12. rpm-ostree-2024.7/src/app/rpmostree-compose-builtin-tree.cxx:1400:5: leaked_handle: Variable "workdir_tmp" going out of scope leaks handle "workdir_tmp.fd".
#  1398|     if (!rpmostreecxx::postprocess_final (rootfs_dfd, **treefile_rs, opt_unified_core, cancellable,
#  1399|                                           error))
#  1400|->     return FALSE;
#  1401|     return TRUE;
#  1402|   }

Reproduction steps

Run coverity against latest release.

Expected behavior

No RESOURCE_LEAK on scans.

Actual behavior

Possible RESOURCE_LEAK

System details

v2024.7 on stream 10

Additional information

No response