Don't crash if compass accuracy is given as none
Don't crash if compass accuracy is given as none

Summary: `metadata.compass_accuracy.value` is required to be float. If accuracy is set to `None`, the if condition passes, but an error is thrown at runtime

Reviewed By: fabianschenk

Differential Revision: D38703925

fbshipit-source-id: 932a3022912b0de640e04102bcd36f5a4070b320

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