Fix #85, Add checks for all return values from fseek()

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to [email protected] and copied [email protected].

Describe the contribution

• Fixes Check Return Value of fseek #85
  • Adds checks for the return from fseek() in 5 locations where this was absent.

Note: in these cases, an error return from fseek() seems extremely unlikely (unless the input data is corrupted somehow) so these checks are mostly just to squash the warnings.

Testing performed
GitHub CI actions (incl. Codeql Build etc.) all passing successfully excl. CodeQL-security for apparently pre-existing issues that are being flagged now.

Expected behavior changes
In cases of error (non-zero) return from fseek() the error info will be printed and early return with FAILED will occur.

Contributor Info
Avi Weiss @thnkslprpt

[jphickey]

See comment, need to double check expected return values from fseek calls

[jphickey]

Shouldn't this be comparing to SeekOffset, not 0? fseek() returns the actual offset in the file on success, or -1 on error. So alternatively it could check for Status < 0. But I think != 0 is incorrect.

[thnkslprpt]

@jphickey
Hi Joe - can you point me to the documentation for fseek() that describes that? - I was definitely under the impression that it returns 0 on success.