getdeps: dyndeps: gracefully handle empty files
getdeps: dyndeps: gracefully handle empty files

Summary:
Don't error out if we can't read the ELF/MACH-O header; just treat
it is not an object.

Reviewed By: chadaustin, simpkins

Differential Revision: D19253434

fbshipit-source-id: c5ecc7f0bc7a20e2611b7e2ff754355155f095da

facebook/folly,facebook/folly,facebook/folly,facebook/folly,facebook/folly