Fixed KeyError during export bundler.

[pulquero]

Fix to avoid KeyError during export bundler. I encountered this error while running a large data set through OpenDroneMap. This fix allowed everything to run to completion with no ill effects on the results afaict. If this error should never happen, then I suggest that this fix be replaced with one that either raises an error that better describes what went wrong or a warning message to that effect and continue.

[facebook-github-bot]

Hi @pulquero!

Thank you for your pull request and welcome to our community. We require contributors to sign our Contributor License Agreement, and we don't seem to have you on file.

In order for us to review and merge your code, please sign at https://code.facebook.com/cla. If you are contributing on behalf of someone else (eg your employer), the individual CLA may not be sufficient and your employer may need to sign the corporate CLA.

If you have received this in error or have any questions, please contact us at [email protected]. Thanks!