Skip Tensor Debug Output population if no buffer is provided (#1421)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1421

Check for Debug Buffer prior to populating

Previously, would error out if debug events were found and debug buffer was not provided

Reviewed By: Olivia-liu

Differential Revision: D52138655

fbshipit-source-id: f706da5c22362de0150a2eaab53ccfd41bfcc8fd