Bugfix: Incorrect stop position is calculated when FSS content ends at the start...

Bugfix: Incorrect stop position is calculated when FSS content ends at the start position on FSS read operations.

When the start position is say, 0, and the determined stop position ends up being 0, then an incorrect stop range is calculated.
This happens because the stop position is subtracting one from the current position.

Add checks to ensure that the stop position is never subtracted beyond the initial start position.

The initial start position is saved at the beginning of each affected FSS read function.

This now potentially returns a start range before the stop range.
The FSS read programs should also need to be updated following this commit to handle these cases.