Make sure array type is bool
Make sure array type is bool

Summary: When the input list is empty, np.array defaults to float type. This causes issue when using the mask for indexing.

Reviewed By: chrert

Differential Revision: D29390081

fbshipit-source-id: 9df5547dd17ca40cb13345f3145b6ff8a04a24bf

mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM,mapillary/OpenSfM