Harden InputMemoryStream Bounds Checks Against Integer Overflow

[jmestwa-coder]

Summary

Harden InputMemoryStream bounds checks against integer overflow when validating read and skip operations.

Changes

• Replace _pos + size <= _size with the overflow-safe form size <= _size - _pos.
• Apply the same validation logic to both CanRead() and Skip().
• Preserve existing behavior for valid inputs while preventing overflow from bypassing bounds checks.

Benefits

• Prevents integer-overflow-induced bounds check bypasses.
• Strengthens validation for untrusted image input parsing.
• Improves memory-safety guarantees across all loaders using InputMemoryStream.
• Centralizes protection in a shared stream primitive rather than individual decoder paths.