grunt.file.recurse dies when working in a directory with an Emacs interlock file

Emacs uses interlock files to prevent simultaneous editing - https://www.gnu.org/software/emacs/manual/html_node/emacs/Interlocking.html

While recursing over directory containing an interlock file, grunt.file.recurse dies with:
Warning: ENOENT, no such file or directory '' Use --force to continue.

Start at the grunt.file.recurse entry point and reproduce the failure with a directory containing an Emacs interlock file. Trace the ENOENT failure during recursion; done means grunt.file.recurse completes without dying when such a file is present.

Written by the indexing model from the issue text.