Fix #1723, Add NULL check for AppFileName parameter in CFE_ES_ReloadApp

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• 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

• Fixes Incomplete OSAL error conversion in CFE_ES_ReloadApp #1723
  • Adds check for NULL input for the 2nd parameter in CFE_ES_ReloadApp() - AppFileName.
    Previously only the 1st parameter, AppID, was directly checked for NULL.

Testing performed
GitHub CI actions all passing successfully. Coverage unaffected.

Expected behavior changes
Will fail faster/earlier with NULL input for AppFileName.
Clearer error logs ease future maintainability and debugging.

Contributor Info
Avi Weiss @thnkslprpt