Fix return type in multiview minimization.
Fix return type in multiview minimization.

keir/libmv,Nazg-Gul/libmv,Nazg-Gul/libmv,keir/libmv,keir/libmv,keir/libmv,Nazg-Gul/libmv,Nazg-Gul/libmv,Nazg-Gul/libmv