[Build] Minimize <iostream> includes #1657 -> fix #1666
[Build] Minimize <iostream> includes #1657 -> fix #1666

Fixing a missing iostream include
- Thx you @bartoszek for the report

openMVG/openMVG,openMVG/openMVG,openMVG/openMVG,openMVG/openMVG,openMVG/openMVG