Fix #34 #37 #43 #44, UT cleanup, remove unreachable code, initialize FileMode on OS_stat failure

[skliper]

Checklist (Please check before submitting)

• [x] I reviewed the Contributing Guide.
• [x] I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fix #34
• Fix #37
• Fix #43
• Fix #44

Testing performed CI

Expected behavior changes Will now initialize FileMode on OS_stat failure (won't write uninitialized data)

System(s) tested on CI

Additional context Can break up if needed, but easier to submit together since they resolve related coverage and UT issues.

Third party code None

Contributor Info - All information REQUIRED for consideration of pull request Jacob Hageman - NASA/GSFC