[CMPMVS] fix spaces troubles in CMPMVS exporter
[CMPMVS] fix spaces troubles in CMPMVS exporter

"P.row(0)" use eigen ostream operator which adds space alignements
between numbers which is not supported by CMPMVS.

poparteu/openMVG,poparteu/openMVG,poparteu/openMVG,poparteu/openMVG